Are the seeds in a single capsicum fruit genetically identical?

Are the seeds in a single capsicum fruit genetically identical?

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Hopefully not a too-basic question for the venue. I'm a chile pepper growing hobbyist and have spent some time searching around and reading up on pepper (angiosperm) reproduction, but I'm not getting a clear picture of the details.

It seems like flowers have multiple ovules and it seems like one pollen-grain landing on the stigma leads to fertilization of a single ovule. And it seems like that process produces a single seed.

But that fertilization also prompts fruit growth and flower death and capsicum fruits have many seeds, never just one (that I've ever seen).

So, does each seed have a potentially different father? Or are the multiple seeds generated through a reproductive/cloning process that I'm not seeing written about? Or something else?

No, the seeds are not genetically identical. Each seed come from the fertilization of an ovum with a sperm from a separate pollen grain. Since each pollen grain can come from a different plant, the seeds will generally differ from one another.

Additionally, even ova from a single plant will not usually be genetically identical to one another. This is because the process that creates the ova (meiosis) shuffles the genes of the parent plant on then places only half into the ovum. The same kind of shuffling goes on in the creation of pollen grains.

In the chili pepper genus (Capsicum), plants are predominantly self-pollinating. This means the majority of the pollen for the seeds in a fruit will come from the very same plant. This generally reduces the amount of variation seen in the offspring compared to complete cross-plant pollination. Some cross-pollination can nevertheless occur if there are other varieties in the neighborhood. The fruit will not show the effects of the new genetic combinations present in its seed, but only a plant grown from the seed will make the differences evident.

Micro-Propagation: Methods and Stages | Biotechnology

In this article we will discuss about:- 1. Methods of Micro-Propagation 2. Stages of Micro-Propagation 3. Advantages 4. Commercial Uses.

Multiplication of genetically identical copies of a cultivar by asexual reproduction is called clonal propagation. The in vivo clonal propagation is often difficult, expensive and even unsuccessful. Tissue culture method offers an alternative way of clonal propagation which is popularly known as micro-propagation.

Here in this method a multiple number of miniatures of vegetative shoots are produced from a clone within a short time and space (Fig. 18.8). Use of tissue culture for micro-propagation was initiated by G. Morel (1960) who found this as the only commercially viable approach for orchid propagation.

The different techniques of single cell and protoplast culture also enable thousand plants to be derived within a short space and time. The products of these rapid vegetative propagation can also be regarded as clones when it is established that the cells they com­prise are genetically identical.

Methods of Micro-Propagation:

(i) Multiplication by Meristematic Tissue of Axillary and Apical Shoots:

Axillary and apical shoots contain quiescent or active meristems depending on the physiological state of the plant. When these shoot tips are cultured on a basal medium containing no growth regulators, these typically develop into single seedling like shoots with strong apical dominance (Fig. 18.9A-B).

On the contrary, when the shoots of the same explant material are grown on culture media containing cytokinin, axillary shoots develop precociously which proliferate to form clusters of secondary and tertiary shoots. These clusters when subdivided and trans­ferred onto fresh medium again these will form similar clusters.

This subdivision process may be continued indefinitely when provided with basic nutrients. About 5-10 multipli­cation rates on 4-8 weeks of micro-propagation cycle may ultimately lead to extremely impressive clonal propagation range of 0.1-3.0 x 10 6 within a year.

(ii) Multiplication by Adventitious Shoots:

Axillary buds are “preformed meristems” present at the leaf axils, whereas adventitious buds may arise from any plant structures and this regeneration is often dependent on the presence of organised plant tissue. The explants may be stems, internodes, leaf blades, cotyledons, root elongation zone, bulb, corms, tubers, rhizomes, etc.

If these explants are induced by using appropriate level of growth regulators in the medium they will form the meristematic zone which regenerates multiple shoots on a suitable culture medium. High number of adventitious shoots may arise only from a single epidermal cell.

Continuous propagation by adventitious shoot proliferation from bulbs and corms can be achieved by cultivating two vertically split piece of shoot bases. Clusters of shoots may develop from the abaxial surfaces of developing leave and scales. Trimming of the shoot apices is a good approach which has been found to ensure continuously productive cultures of different hybrid plants for indefinite period.

(iii) Multiplication by Adventitious Embryo Formation:

It is another useful approach followed for many important plant species. Adventitious embryos can arise directly from a group of cells within the original explants or from primary embryoids.

There are many plant species which develop embryos in vivo from diverse kind of explants e.g. the orchid leaf tips produce large number of embryoids whereas Citrus and Mangifera have shown to develop polyembryos from nucellar tissue.

These adventitious embryoids are diploid in nature and can be used as clonal material for micro-propagation. In in vitro similarly the adventitious embryos originated from different explants can be good materials for clonal propagation.

(iv) Multiplication through Callus Culture:

Direct plantlet formation from the explants in culture is more desirable in case of micro- propagation or clonal propagation. But shoot formation may occur through organogenesis or embryogenesis from the callus produced from the explant.

The limitation of this system is that the callus cells are not geneti­cally stable so it cannot be called as a single clone and this process is more time consum­ing. Also the plant regeneration capacity may decline due to the genetic unstable condition.

In case of some plant species genetically stable calli have also been derived, in these types of calli slow growing meristematic zones are formed from the peripheral layer. The meristematic layers invariably comprise of diploid cells expressing totipotency. These types of calli can be subdivided into smaller parts and which may produce multiple shoots from each.

Stages of Micro-Propagation:

The process of micro-propagation or clonal propagation is a complicated process which can be subdivided into four prominent stages of operation:

This is the initial step of micro-propagation in which stock plants has to be j grown under controlled condition before using for culture initiation.

The preparation of explants from stock plants is followed by its establishment j in a suitable culture medium.

The steps involved in this stage are:

(d) Establishment of explant on appropriate culture medium.

This stage involves the multiplication of shoots or rapid somatic embryo formation using a defined culture medium.

Various Approaches followed for Micro-Propagation Include:

(i) Multiplication through the growth and proliferations of meristems excised from apical and axillary shoot of the parent plant.

(ii) Induction and multiplication of adventitious meristems through proces­ses of organogenesis or somatic embryogenesis directly on explants.

(iii) Multiplication of calli derived from any kind of explant and subsequently shoots development either through organogenesis or embryogenesis. The harvest cycle generally takes 4-8 weeks. Either the shoots are marketed directly or carried over to the next stage for further development.

Shoots obtained from stage II are transferred to the next rooting or storage medium. These shoots are directly established in soil as micro-cuttings to develop roots. The shoot handling at this stage differs from species to species.

When the shoots are directly transferred to soil then the following procedures are to be maintained:

(i) Each shoot should be rooted individually,

(ii) Hardening of the shoots to increase their resistance,

(iii) Allowing the plants capable of autotrophic development rather than the heterotrophic development in culture,

(iv) Fulfilling the requirements for breaking dormancy.

Transfer of plantlets to sterilized soil for hardening under greenhouse environ­ment is achieved. This step is to ensure the successful transfer of the plantlets of stage III or un-rooted shoot apices of stage II into the suitable compost mix­ture or soil in pots under controlled condition of light, temperature, humidity.

For marketing sometimes these plat lets are established in an artificial grow­ing medium such as soil-less mixes, Rockwood plugs or the sponges. It takes 4-16 weeks for marketing of the finished products.

Advantages of Micro-Propagation:

1. The technique of micro-propagation is an alternative approach to conventional methods of vegetative propagation, which has the enhanced rate of multiplication.

2. A million of shoot tips can be obtained from a small, microscopic piece of plant tissue within a short period of time and space.

3. The advantage in this type of propagation is that as shoot multiplication usually has a short cycle (2-6 weeks) and each cycle results in logarithmic increase in the number of shoots.

4. This method of propagation is more advantageous in case of bulb or corm pro­ducing plants, because mini-tubers or mini-corms for plant multiplication are available throughout the year irrespective of season.

5. Smaller size of propagules are advantageous for storing and transporting as it takes lesser space.

6. The propagules can be maintained in soil-free environment which facilitates their storage on a large scale.

7. Stocks of germplasm can be maintained for many years using this method of propagation.

8. This method is more applicable where disease free propagules are wanted. This in vitro technique helps to raise pathogen free plant and to maintain them.

9. Micro-propagation is very useful in case of dioecious plants, because there the seed progeny yield is 50% male and 50% female, but this technique helps to get the progeny according to the desired sex.

10. A major advantage of micro-propagation happens to be the minimum growing space required in commercial nurseries. Thousands to millions of plantlets can be maintained within the culture vials. This is specially useful for maintaining the horticultural species.

11. This method is more helpful in case of slow growing plants where the seeds are produced after a long term and the seeds are the only propagule. This method can overcome the difficulty to obtain the propagules.

12. Through seed production genetically uniform progeny is not possible always. But the micro-propagation method will help to maintain the genetic uniformity in the propagules.

13. Micro-propagation is one of the finest ways of plant multiplication by in vitro technique of plant tissue culture. The newer tissue material obtained through r DNA technology or haploid culture or somatic hybridization can be the source of tissue material for micro-propagation, as it is the easiest method for obtaining the multiple propagules.

Commercial Uses of Micro-Propagation:

Micro-propagation of orchids demonstrated profit all over the world, besides orchid about 600 species of other ornamental plants have been successfully cloned and some of them are commercially exploited (Chrysanthemum, Carnation, Gerbera and Anthurium), list of names is increasing day by day, the advantage is rapid cloning of selected colour individuals.

Except the horticultural flowering plants, a large number of forest trees, fruit trees, oil producing plants (Eucalyptus, Oil-palm), vegetables and many edible crops like peach, apple, pear, cherry, apricot and palm have been cloned and put into use commercially (Fig. 18.10).

Breeding and selection by sexual hybridization is a very slow procedure because of long generation time and they are difficult to propagate vegetatively. So the in vitro cloning of more than 100 woody species over a wide range of families has been successfully achieved.

Forest trees are important sources of our biodiversity and also they provide food, fuel, construction and industrial products for us.

These resources are diminishing at an unprecedented rate. Large scale, cost-effective and nursery-friendly in vitro technique like micro-propagation protocols have been developed for selective forest trees about 70 forest tree species of Angiosperm and about 30 forest tree species of Gymnosperm.

The most important aspect of commercial micro-propagation is the economics involved and the unit cost of a plantlet. Research achievements in the field of micro-propa­gation are not always economically viable and not accepted by commercial houses. The investment in commercial tissue culture business will depend to a large extent on cost of the laboratory set up, type of plant to be propagated and the skill involved.

The commercial nursery man should start with those crop species for which pub­lished methods are available and also it is essential that the grower must have some training in tissue culture and plant husbandry. Another approach followed in micro- propagation is to automate it at its various stages.

In this connection the bioreactors are being used for large scale multiplication of somatic embryos, shoots and bulbs. Automatisation have also been used for subculture of shoots during stages III and IV of micro-propagation. This reduces the cost of labour component in micro-propagation.

Are the seeds in a single capsicum fruit genetically identical? - Biology

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Agricultural Genetic Resources Preservation Research: Fort Collins, CO

General preservation questions:

What are genetic resources? Genetic resources are living material such as crops, livestock, related species, rare and endangered varieties and breeds that include genes, genetic combinations (a.k.a. genotypes) or genetic frequencies that give diversity to future varieties or breeds. In agriculture, genetic resources are used by breeders to increase yields and stress tolerance, improve nutrition, and add value, beauty, flavor, and adaptability.

What is germplasm? Germplasm is a set of propagules that carries the desired genetic resource (i.e. genes, genetic combinations or gene frequencies).

What is an accession? An accession is a genetically unique plant sample from a particular geographic location. At NLGRP, an accession may be a bag of seeds, plant tissue cultures, or buds from twigs of fruit crops. NLGRP sometimes stores more than one sample of a particular accession. When samples are regrown or reproduced, the subsequent generation has the same accession number as the parent sample. The new sample has an inventory number that identifies the generation number.

What is a propagule? A propagule is a tissue, organ or plant part that can be regenerated into a whole plant (i.e. seeds, cuttings and budwood).

What is genetic diversity? Genetic diversity is variation in life that is heritable. Modern crops or livestock breeds may have a low amount of diversity because of repeated selection for desirable traits and widespread use of few individuals or varieties. Populations become diverse through the processes of mutation and sexual reproduction. Natural selection acts on this diversity to favor the changes that enable the best survival in a particular environment. Populations that have a lot of genetic diversity can survive dynamic environments better than populations that have low genetic diversity. Genetic diversity is what enables breeders to improve plant varieties and animal breeds.

What is a clone? A clone is a group of genetically identical cells descended from a single common ancestor one or more organisms descended asexually from a single ancestor one that is an exact replica of another (Webster II. The Riverside Publishing Company, 1984).

What is cryopreservation? Cryopreservation is a process of cooling cells or various kinds of tissues to temperatures below zero to slow down effectively life processes without damage to the material. Plant tissues or plant cells are usually cryopreserved at liquid nitrogen (-196 o C) or vapor of liquid nitrogen (ca. -156 o C).

What are plant tissue cultures? Plant tissue cultures are plant tissue, cells or plant organs maintained or propagated in vitro under aseptic conditions on sterile culture medium. This method of plant propagation is referred often as micropropagation. Plants derived from one original propagule (plant, tissue or cell) are clones.

What is a recalcitrant seed? A recalcitrant seed, in contrast to most crop seeds, is a seed that cannot survive drying and so cannot survive in the freezer. Preservation of recalcitrant seeds requires a procedure that prevents damage by drying or freezing. This has been accomplished in several species by excising the growing part of the seed, optimizing the water content, and cooling very rapidly. Recalcitrant seeds are frequently produced by temperate-zone forest trees, riparian species, and plants from the tropics. Examples of recalcitrant seeds are oak seeds, wild rice, and citrus.

Why is the NLGRP located in Fort Collins, Colorado? The dry climate was a primary reason that the USDA National Seed Storage Laboratory (NSSL) was located in Fort Collins, CO. With an average relative humidity of about 30%, little effort was needed to adjust seed moisture content to the optimum level needed for long-term storage. In the 1950s a Colorado State University professor, Dr. D.W. (Scotty) Robertson, was very active in promoting germplasm preservation. A barley breeder, Dr. Robertson, argued that a base collection for genetic resources should be established and worked to have the Laboratory built on the Colorado State University campus. The Beet Sugar Development Foundation also supported these efforts.

What is the NLGRP capacity? The NLGRP has capacity to store between one and 1.5 million accessions, depending on the size of the propagule, in storage vaults cooled to -18 o C (conventional storage). In addition, the NCGRP has a 220 cryotank capacity, with each cryotank holding about 3,000 seed and 70,000 semen accessions.

How safe are the collections? The facility has protected access to all work areas in the building. The storage areas , including the seed cold vaults and cryogenic room, are further restricted by added security with limited access of only a few individuals, additional locked doors, security cameras, and coded information on sample bags. The vault area is fortified against tornadoes and floods and there are backup mechanical systems.

Can anyone get seeds from NLGRP? Distributions are made for research purposes from the NPGS sites located around the US.

Where does the germplasm come from and who donates it? Germplasm comes from all over the world and it is donated by collectors, breeders or experts in systematics who locate material with unusual or interesting traits that may eventually be useful in agriculture. For example, a collector may find an apple with unusual flavor or a wheat landrace that is resistant to aphids. Most of the germplasm for agricultural crops comes from the area where that crop evolved. This area, known as the Center for Diversity, is believed to have the highest genetic variability in the smallest geographic area.

Does NLGRP save endangered plant species? In collaboration with conservation groups, we store seeds of endangered species. This activity can preserve the remaining genetic diversity of an endangered species until it is reintroduced into native habitats.

How large is the NLGRP plant collection? There are more than 500,000 accessions in the collection. Each accession contains about 3,000 to 5,000 seeds, depending on the reproductive biology of the species.

How many species are in the NLGRP plant collection? About 12,000. Changing needs for US agriculture and landscapes will lead to an inevitable increase in the numbers of species collected and stored at NLGRP.

How do I request germplasm? Search and request germplasm using GRIN-Global.

What is the best way to store seeds? Allow seeds to dry for a few weeks in a place with about 20% relative humidity. Then store seeds in vapor-proof containers such as a glass jar or sealed moisture-proof bag in a cold place like a home freezer.

How long can seeds survive in storage? Seed longevity depends on storage conditions and seed quality. We expect most undamaged seeds that are properly dried to survive about a hundred years in conventional storage (-18C) and about a thousand years under cryogenic (liquid nitrogen) conditions.

What is the oldest living seed? The most reliable studies show some seeds in soil at archeological sites surviving for 100 to 1,700 years. (e.g. Odum 1965. Germination of ancient seeds: floristical observations and experiments with archaeological dated soil samples. Dan. Bot, Arkiv 24(2):1-70 Shen-Miller, J., Mudgett, M.B., Schopf, J.W., Clarke, S., and Berger, R. 1995. Exceptional seed longevity and robust growth: Ancient sacred lotus from China. American Journal of Botany).

How long does DNA last? DNA, the genetic code, found in all life, is a very stable molecule. Fragments that are thousands of years old have been found in archeological artifacts, especially if the artifacts have been kept dry or free from microbes that cause decay.

Can I plant seeds from an apple I really enjoyed? You can plant seeds from that apple and get a tree in about 5-10 years, but the fruit from the new tree will not be the same as the apple that you enjoyed. This is because fruit quality is specific to the mother plant, and the mother tree and the offspring tree are genetically different. Most fruit crops must cross-pollinate to produce seeds. For fruit crops, the same genetic line is usually maintained by grafting budwood from the mother plant onto a rootstock or rooting stems that are cut from the mother plant.

Seminal Science: How Many Seeds Do Different Fruits Produce?

Do you like your strawberry jelly with or without the seeds? Are you glad to have a seed-free watermelon, or do you enjoy spitting the seeds into the garden? You might not like finding seeds in your fruit, but fruit is a plant's tool for dispersing seeds to create offspring. In this activity you will investigate how many seeds can be dispersed for each type of fruit. Based on the number of seeds they produce, how productive do you think some of your favorite fruits are?

Many plants grow fruit to enclose and protect their seeds, which need to spread out to grow new plants. Animals love to eat sweet, juicy fruit. This approach would seem like a poor way for plants to protect their seeds, so why would making fruit that is tasty be beneficial? When an animal eats fruit the fleshy part is digested. The seeds, however, pass without harm through the digestive system and are spread by the animal when it excretes (poops). In this way, they are deposited farther from the original plant (along with a little bit of fresh fertilizer) and can grow into a new plant. This is called seed dispersal, and it is just one strategy that plants use to spread seeds over a wide area and make more plants.

You might think that all fruit-bearing plants would pack as many seeds as possible into each fruit to maximize the number of new plants that will grow. But, in fact, different plants have different strategies for seed production and dispersal. Some fruits produce many, many seeds to make sure that at least some will grow, even if most fail. Other fruits put all of their resources into producing and protecting one very large seed.

&bull Different types of fruits: Try to include a pepper, tomato and apple as well as a squash or cucumber (yes, all of these are technically considered the "fruits" of their plants)
&bull Knife
&bull Cutting board
&bull Paper towels

&bull Go to the grocery store and pick out different kinds of fruit. Don't just stick to traditional fruits, try some new ones as well. Some produce you might think are vegetables are really fruit! Try to include at least one pepper, tomato and apple, along with a squash or cucumber. Avoid seedless varieties.
&bull Tip: Bananas do have seeds, but they are very tiny, appearing as little black spots in the center of a banana slice. You can try to count them, but it is not recommended!
&bull Tip: If you dissect a pepper, be sure to wash your hands before you touch your eyes after handling the seeds. Pepper seeds can be spicy and cause a burning sensation! Use a mild pepper variety, such as a bell pepper, if you are very sensitive.
&bull You may need an adult to help you when cutting the fruit open.

&bull Begin to dissect your first fruit, removing the seeds and placing them on a paper towel. In the fruit, are the seeds arranged in a certain pattern?
&bull When you are done removing the seeds, count the number of seeds on the paper towel. How many seeds were in the fruit?
&bull Tip: If you are dissecting a cucumber or squash, instead of removing the seeds you can try cutting the fruit lengthwise, counting the rows of seeds, and then slicing the fruit the other way to determine how many seeds are in one row. Multiply these two numbers together to get a good approximation of the total number of seeds.
&bull One at a time, continue to dissect each fruit, place the seeds on a paper towel, then count them. Be sure to keep the seeds from different fruits separated.
&bull How many seeds are in each fruit? Which held the most seeds? The least? Did similar types of fruit produce similar numbers of seeds?
&bull How do seeds from different types of fruit look similar or different? In each fruit, were there similar patterns in which the seeds were arranged?
&bull Extra: Try this activity again but use multiple fruit of each type, such as multiple peppers, tomatoes, cucumbers and squash. Does the same type of fruit always hold a similar number of seeds, or does the amount vary a lot?
&bull Extra: Is fruit size related to seed quantity? Repeat this activity but this time use a ruler to measure each fruit before you count their seeds to see if larger fruits tend to produce more seeds than smaller ones. (You can also use a scale to weigh each fruit as an alternative way to measure fruit size.) Do larger fruits make more seeds?
&bull Extra: Are seedless fruit varieties really seedless? Dissect several different varieties of seedless fruits and look for seeds. Are "seedless" fruit varieties completely seedless, or simply have fewer seeds than normal? What is the decreased seed productivity of seedless varieties compared with normal varieties on a fruit-to-fruit comparison basis?

Observations and results
Did some types of fruit clearly have more seeds than others? Did the cucumbers, squash, tomato and pepper have a lot of seeds, easily over 100 each? Did the apple only have a few seeds, no more than 10?

Fruits are divided into three general groups, with the "simple fruits" group making up the majority we encounter. They're formed from one ovary in one of the plant's flowers. As the ovary turns into fruit, different ovary parts become different fruit parts when fertilized, small structures called ovules become the fruit's seeds&mdashand more fertilized ovules means more seeds! The other two fruit groups are more complex. In "aggregate fruit"&mdashsuch as raspberries&mdashmultiple ovaries fuse on a single flower. In the third group, called "multiple fruit," many ovaries and flowers unite. A pineapple is a good example of a "multiple fruit."

Cucumbers, melons and squash are simple fruits (they are part of a fruit type called pepo, which are berries) with a firm rind and softer, watery interior. And, as you probably saw, these fruits make many seeds! A zucchini or cucumber can easily have a couple hundred neatly patterned seeds.

Tomatoes, grapes, kiwifruit and peppers are also simple fruits (technically true berries) with fleshier walls and usually very fluid insides&mdashthink of how watery a ripe tomato is! Some, like tomatoes and peppers, can have a couple hundred seeds, whereas others, like kiwifruit, can have several hundred! Citrus fruits are berries (a type called hesperidium), too, with leathery rinds and usually only a few seeds.

Similarly, apples and pears also only have a few seeds (10 at most) but are not berries&mdashthey belong to a different fruit type, known as pomes, which have some fruit flesh not made from the flower's ovary, but rather from plant tissue near the ovary, which is the same for strawberries.

Dispose of the seeds from your fruit or, if you're motivated and curious, look into how you could grow plants from your seeds. You can eat the rest of the fruit or save it for a tasty, healthy snack later!

This activity brought to you in partnership with Science Buddies

Why do all fruits have seeds?

Fruits have a very important job to do in nature – much more important to the plant than just feeding nearby insects, birds, animals or people!

The seeds hidden inside of each fruit have everything they need to grow into a new plant and ensure the survival of that plant species.

To ensure its seeds will get planted and have the chance to grow, the plant produces a tasty outer fruit around its seeds to encourage insects and birds and other animals to eat the fruit and then distribute the undigested seeds.

This is also why the seedless fruits mentioned in the previous section here don’t typically occur in nature – farmers must genetically manipulate their plants in some way to get them to produce seedless fruits.

Plants that produced seedless fruits in nature would quickly be in danger of dying out!

Are the seeds in a single capsicum fruit genetically identical? - Biology

Offspring of any organism, if they are not clones, differ from each other. Seeds produced by a mother plant are no exception, and they vary in size, color and shape. Usually, these differences are minor and represent a continuum of gradual changes, but some plant species produce several categories of distinctly different seeds. This phenomenon is called discrete heteromorphism. An example is a production by a single plant two kind of seeds: seeds having a special structure for wind dispersal called pappus and those without pappus. Production of two kinds of seeds has a functional importance: while some seeds stay at the place of origin, others are dispersed away from it.

Another kind of seed heteromorphism, when seed can not be categorized into several distinct classes of shape, color or size, called continuous heteromorphism, until recently was thought to be purely a result of developmental variation. Seeds within the fruit, inflorescence or dispersal unit can compete for available resources, and as a result be larger or smaller. This explains, for example, why seeds of flowers at basal positions, which are the first-formed and therefore better-developed are usually larger than seeds of flowers at distal positions.

The question that we asked was whether this variation is only a by-product of seed developmental process within a plant or has some functional importance for a plant and as such became a target for natural selection.

Wild wheat, a progenitor of cultivated wheat that grows in Near East and Turkey, produces spikes that at maturity disarticulate into arrow-shaped spikelets. Each spikelet comprises 2- or rarely 3-grains. Grains of different position within a spikelet slightly differ in size, but, as we have shown in a series of experiments, differ in germination pattern under both field and controlled conditions. The upper grain in a spikelet is larger than the bottom grain, and either germinates in the season following dispersal, or dies. In contrast, a substantial fraction of the bottom grains does not germinate in the first season, but remains dormant in the soil seed bank for one year.

The two grain difference in dormancy can not be explained by a competition for resources alone. When plants are grown in a greenhouse, resources are in good supply, and competition for them between the two grain types is unlikely or minor. Under these conditions the difference in size between upper and bottom grain is subtle but a difference in grain dormancy is retained.

Theoretically, production of both dormant and non-dormant seeds can help to deal with environmental unpredictability, when some seeds will stay dormant in the soil in a year when amount of rainfall is below a threshold for plant survival and reproduction allowing population persistence. In this case a higher proportion of dormant seeds can be more important and selected for under higher aridity. Another hypothesis relates production of both dormant and non-dormant seeds to competition among the offspring in species with low seed dispersal ability. This hypothesis predicts higher importance of production of two kind of seeds in more productive environment because in this environment competition is more intense.

We found some increase in seed dormancy of the bottom grains with increase in aridity of their locations, but high seed dormancy was present in spikelets of all origins.

It seems that seed polymorphism can not be attributed to a single evolutionary cause, and is a life history trait with complicated evolutionary history and wide adaptive applicability. Seed polymorphism appears to originally evolve as an adaptation for reducing competition in productive (high precipitation) environments, and under increasing aridity became important for surviving periods of insufficient rainfall.

Sergei Volis
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany,
Chinese Academy of Sciences, Kunming, China

Sources of Seedlings

Mississippi landowners have several sources for seedlings. MTN 4E Forest Seedling Availability from In-State and Regional Nurseries lists several nurseries in Mississippi and neighboring states. You can request a copy of this list by emailing [email protected]

Remember that it is your responsibility to be informed about seedlings you order. It is also important to order seedlings early because nurseries often sell out by planting season. If you are planning to use state or federal cost-share funds or the Mississippi reforestation tax credit for forest tree planting on your land, an MFC area forester must approve the source of your seedlings.

The Capsicum Genus

Capsicum terminology is very confusing with Pepper, chilli, chile, chili, aji, paprika and capsicum all used interchangeably to describe the plants and pods of the genus Capsicum. We have chosen to use 'chile' as this is the most common terminology used in the UK. It is believed Chiles were first cultivated by the people of Central and South America in around 7000BC and there are now a bewildering range of over 3000 known varieties ranging from the mildest bell pepper to the fiery hot habanero. The botantical 'genus' to which all chiles belong is Capsicum (CAP-see-coom), from the greek kapto meaning 'to bite'. The genus Capsicum is also a member of the wider Solanaceae or nightshade family and therefore Chile peppers are closely related to their genetic cousins, the tomato, potato, tobacco and eggplant. Ever since, English doctor turned botanist Robert Morrison described 33 species of Chile peppers in his study, 'Plantarum Historiae Universalis Oxonniensis', published in 1680, there has been much argument and debate amongst botanists and taxonomists as to the number and classification of Capsicum species.

After much argument and amendment, it is now widely accepted that the genus Capsicum consists of five domesticated species and twenty-six wild species. Due to the ease at which the domesticated species in particular cross pollinate with each other and the active development and hybridisation of new varieties often for marketing purposes, there is now a baffling range of varieties available making classification and increasingly difficult task. More detailed information and picture illustrations of each of these species and their numerous cultivars can be found in thechileman's database. To refine your search, be sure to select the appropriate species from the drop down list. The five domesticated species Annuum, Baccatum, Chinense, Frutescens and Pubescens are the most commonly available species to the Chile enthusiast and each species has its own distinguishing characteristics.

Capsicum Annuum (ANN-you-um)

Annuum meaning 'annual' is actually an incorrect designation given that Chiles are perennials under suitable growing conditions. This species is the most common and extensively cultivated of the five domesticated species and includes the Ancho, Bell Pepper, Cayenne, Cherry, Cuban, De Arbol, Jalapeno, Mirasol, Ornamental, New Mexican, Paprika, Pimiento, Pequin, Serrano, Squash and Wax pod types.

Annuum's used to be dividend into two categories, sweet (or mild) peppers and hot Chile peppers. However, modern plant breeding has removed that distinction as hot bell varieties and sweet Jalapenos have now been bred.

Capsicum Chinense (chi-NEN-see)

Chinense meaning 'from China' is also a misnomer as this species originated in the Amazon Basin and is now common throughout the Caribbean, Central and South America and in the tropics.

This species includes many of the world's hottest cultivars including the Habanero, Scotch Bonnet and the legendary Red Savina. The pod types, as well as the plants are very varied in this species although they are characterised by a distinctive fruity aroma often described as apricot like.

The Chinense being a tropical species tend to do best in areas of high humidity. They are relatively slower growers, having longer growing seasons than many of the other species and seeds can take a long time to germinate.

Capsicum Baccatum (bah-COT-tum or bah-KAY-tum)

Baccatum meaning 'berry-like' consists of the South American cultivars known as Aji's. They are almost as many baccatum cultivars as annuums with pods ranging from non-pungent to very hot.

The baccatum species is generally distinguished from the other species by the yellow or tan spots on the corollas (on the flowers) and by the yellow anthers. Many of the baccatum species are tall growing, often reaching 5 feet in height and pods are usually erect and become pendant as they mature.

Capsicum Frutescens (fru-TES-enz)

Frutescens meaning 'shrubby' or 'bushy' is not widely cultivated with the exception of the Tabasco, which has been used in the manufacture of the world famous sauce since 1848. Another famous variety is the Malagueta, which grows in the amazon basin in Brazil where the species probably originated.

Frutescens plants have a compact habit, have many stems and grow between 1 and 4 feet high depending upon local conditions. The flowers have greenish white corollas with no spots and purple anthers. Pod types are less varied than the other species (with the exception of Pubescens) are often small, pointy and grow erect on the plants. This species is particularly good for container gardening and a single plant can produce 100 or more pods.

Capsicum Pubescens (pew-BES-enz)

Pubescens meaning 'hairy' is probably the least common on the five domesticated species and is the only domesticated Capsicum species with no wild form. However two wild species 'Cardenasii' and 'Eximium' are believed to be closely related. Pubescens has a compact to erect habit (sometimes sprawling and vine like) and can grow up to 8 feet tall, although 2 feet is more usual. The flowers have purple corollas, purple and white anthers and stand erect from the leaves. The pods are normally pear or apple shaped.

One interesting point to note is that the species is 'isolated' from the other domesticated species as it cannot cross pollinate with them. Another distinguishing feature of the species is the black seeds of the fruits. Varieties include the Peruvian 'Rocoto' and the Mexican 'Manzano'. Probably the most difficult of the five domesticated species to grow.

The Wild Species

The twenty six wild species lack extensive study on their biology and seeds are much harder to come by as they are often subject to restricted seed distribution. An interesting generalisation is that most of the wild Chile species have small fruits, which are eaten with ease by birds the natural dispersal agent for Capsicum species. The 23 widely recognised wild species are:


A wild Chile species native to Brazil.


A recent classfication (2011) from north east Brazil.


A wild Chile species native to Southern Brazil


A tubular purple flowering wild species native to La Paz, Bolivia. Genetically it is part of taxa including Capsicum pubescens and is more commonly known as 'Ulupica'.


A small white flowering wild species native to Argentina, Bolivia and Paraguay. It is known locally as 'Tova' in Paraguay. The Plant has an erect growing habit and is approximately 80 cm tall. The erect pods are elongated, triangular, 2.5 cm long, 0.5 cm wide and mature from green to red. Very scarce.


A white flowering wild Chile species native to Bolivia and Peru.


A wild Chile species native to Southern Brazil.


A wild Chile species native to Colombia.


A wild Chile species native to south-east Brazil.


A white flowering wild species not commercially grown, although several Chile enthusiasts have successfully grown the cultivar 'Cobincho'. This plant is very unlike most other capsicums. Plants can grow to over 130 cm tall with small, smooth leaves.


A purple flowering wild species native to Bolivia and northern Argentina. Said to be a wild relative of the Rocoto. Genetically part of taxa including Capsicum pubescens and said to grow like a small tree.


A white flowering wild species native to the Galapagos Islands of Isabela and Santa Cruz. Also found in Ecuador. The pods of this plant are very hot and grow to 0.25 inches long, maturing from dark green to red.


A wild Chile species native to Colombia and Ecuador.


A wild Chile species native to Ecuador.


A wild Chile species native to Guatemala, Honduras and Mexico.


A wild Chile species native to Brazil.


A recent classfication (2011) from north east Brazil.


A wild Chile species native to Argentina, Bolivia and Paraguay.


A wild Chile species native to southern Brazil.


A wild Chile species native to north-east Brazil, Colombia and Venezuela.


Sold commercially in parts of Brazil and also known as Capsicum baccatum var. praetermissum. This variety can grow up to six feet tall in a single growing season and has hundreds of cranberry sized fruit that ripen to red. The flowers are totally flat when fully opened, are purple edged with a white inner band and have a greenish yellow centre. The ripe fruits are said to be very seedy.


A very unusual and scarce wild Capsicum species initially believed to be a sister to Capsicum Tovarii although after further study by Eshbaugh in 1988, it has since been omitted from Capsicum species list. Native to Southern Mexico & South America, this species has pubescent stems and leaves and yellow flowers. The tiny red fruits have no heat. Now a synonym for Witheringia ciliata although more recently it has been reclassified (yet again) as Capsicum rhomboideum.


A wild Chile species native to Argentina, south Brazil and south-east Paraguay. These 80-100 cm tall erect plants have many branches which grown in a zig zag pattern. The flowers are white with yellow-green spots at the base of the petals. Fruits are pendulous and reddish-orange at maturity.


A wild Chile species native to Peru.


A purple flower wild species native to the Rio Mantaro basin in south-central Peru. Genetically part of taxa including Capsicum pubescens.


A wild Chile species native to southern Brazil.

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Search Database

Use the following short form to search 3812 types of pepper by name, heat, origin and genus.

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So Spicy!

Although there are varieties that are not spicy, such as sweet peppers, spiciness and heat are the qualities most desired by chili eaters. &ldquoThe hotness of chilies is caused by alkaloids known as capsaicinoids. They were developed to prevent mammals from eating the fruits and thus destroying the seeds in their digestive tract,&rdquo Bosland explains. This problem does not happen when birds eat the fruits, however, and they have helped spread the genre across America.

Although Grabiele did not focus his research on the spiciness, he discovered that C. rhomboideum, whichproduces fruits without spiciness, has very different chromosomes from the rest and a genome three times smaller. &ldquoThis pepper, which is not hot, was separated early from the rest of peppers 15.6 million years ago, very close to the emerging of the genre. As all the other peppers have spicy fruit and share their last common ancestor 13.8 million years ago, that time would be the onset of spiciness for peppers,&rdquo he says.

According to Bosland, chilies could be one of the first crops domesticated in America because it dates back 10,000 years ago. &ldquoAssociations of corn, peppers and ceramics were found in some regions of the continent showing that corn and chili occurred together as an ancient food complex,&rdquo he says.

Domestication occurred independently in different places for the five cultivated chili species. Current thinking suggests that C. annuum was first domesticated in Mexico. A study published in Proceedings of the National Academy of Sciences in 2014 determined that the origin of this species was in east-central Mexico, farther south than previously thought and in a different region from where corn and bean crops originated.

Meanwhile, C. frutescens was domesticated in Central America C. chinense, in the Brazilian Amazon C. baccatum, in Peru and C. pubescens in Bolivia. In Peru the oldest archaeological remains that prove their presence were found in Caral, thought to be the oldest civilization in the Americas.

Lecture 12: Genetics 1—Cell Division and Segregating Genetic Material

In this first lecture on genetics, Professor Martin talks about how information flows between cells, such as from parent cells to daughter cells. He also talks about information flows from one generation to the next, ending lecture with a demo.

Instructor: Adam Martin

Lecture 1: Welcome Introdu.

Lecture 2: Chemical Bonding.

Lecture 3: Structures of Am.

Lecture 4: Enzymes and Meta.

Lecture 5: Carbohydrates an.

Lecture 9: Chromatin Remode.

Lecture 11:Cells, The Simpl.

Lecture 16: Recombinant DNA.

Lecture 17: Genomes and DNA.

Lecture 18: SNPs and Human .

Lecture 19: Cell Traffickin.

Lecture 20: Cell Signaling .

Lecture 21: Cell Signaling .

Lecture 22: Neurons, Action.

Lecture 23: Cell Cycle and .

Lecture 24: Stem Cells, Apo.

Lecture 27: Visualizing Lif.

Lecture 28: Visualizing Lif.

Lecture 29: Cell Imaging Te.

Lecture 32: Infectious Dise.

Lecture 33: Bacteria and An.

Lecture 34: Viruses and Ant.

Lecture 35: Reproductive Cl.

ADAM MARTIN: Well, first of all, nice job on the exam. We were quite pleased with how you guys did. And so from now on in the course, Professor Imperiali has been telling you about information flow, but information flow within itself, so information flow from the DNA to the proteins that are made in the cell, which determines what that cell does. And so we're going to switch directions today. And we're going to start talking about how information flows between cells-- so from a parent cell to its daughter cells. And we're also going to talk about how information flows from generation to the next.

And this, of course, is the study of genetics. And what genetics is as a discipline is it is the study of genes and their inheritance. And the genes that you inherit influences what is known as your phenotype. And what phenotype is is simply the set of traits that define you. So you can think of it as a set of observable traits.

And this involves your genes, as you probably know. I mean, just this morning, I was dropping my son off at school, and he was comparing how tall he was compared to his classmates. And as he went in, he was like, thanks for the genes, dad. So I expect that many of you are going to be familiar with much of what we'll discuss, but we're going to lay a real solid foundation, because it's really fundamental for understanding the rules of inheritance and how that works.

So genetics is the study of genes. So what is a gene? You can think about genes in different ways. And what we've been talking about up until now, we've been talking about molecular biology and what is known as the central dogma. And the central dogma states that the source of the code is in the DNA. And there's an information flow from a piece of DNA, which is a gene. And the gene is a piece of DNA that then encodes some sort of RNA, such as a messenger RNA. And many of these RNAs can make specific proteins that do things in your cells in your body. So that's one very molecular picture of a gene.

You can think of a gene as a string of nucleotides. And there might be a reading frame in those nucleotides that encodes a protein. So that's a very molecular picture of a gene. The field of genetics started well before we knew about DNA, and its importance, and what the DNA encoded RNA which encoded proteins. So the concept of a gene is much older than that.

And so another way you can think of a gene is it's essentially the functional unit of heredity. So it's the functional unit of heredity. I'll bump this up. So I want to just briefly pause and kind of give you an overview of why I think genetics is so important.

So what you saw up here is you saw a cell divide. And I showed you this in the last lecture-- you saw the chromosomes, which are here, how they're segregated to different daughters. And this is-- basically, you're seeing the information flow from the parent cell into the daughter herself. But we saw this, so I'm just going to skip ahead.

So why is this so important? I'm going to give you a fairly grandiose view of why genetics is so important. And I'm going to say that we can make a good argument that genetics is responsible for the rise of modern civilization. Humans, as a species, began manipulating genes and genetics even before we had any understanding of what was going on. So this is more of an unconscious selection.

And so 10,000 years ago, humans were hunter gatherers. They'd go out, and try to find nuts and seeds, and hunt animals. And that's how we got our food. But around 10,000 years ago was the first example of where humans, as a species, really altered the phenotype of a plant, in this case. So wild wheat and wild barley, the seeds develop in a pod. And the biology of the wild wheat is such that the pod shatters, and the seeds then spread on the ground where they can then germinate into new plants.

But 10,000 years ago, humans decided that it would be more ideal if we had a form of wheat which didn't shatter, which is known as non-shattering wheat in which the seeds remain on the plant. And that allows it to be easily harvested at the end of the season. So 10,000 years ago is one of the first examples where humans really genetically altered the phenotype of a plant. And they selected for this non-shattering wheat, which then allowed for the rise of agriculture.

In addition to wheat, we also-- about 4,000 years ago was the rise of domesticated fruit and nuts. So here are some almonds. If you would like an almond, feel free to have some. You guys want some almonds? No. If you have a nut allergy, don't eat them. Great.

So wild almonds, when you chew them, there's an enzymatic reaction that results in cyanide forming. Rachel just stopped chewing. Don't worry. These are almonds that are harvested at Trader Joe's, so you're safe. And so the wild almonds, obviously, were not compatible for consumption. But 4,000 years ago, humans again selected for a form of the almond, which involved just a single gene, which was non-bitter and known as a sweet almond, which was also not toxic.

So this doesn't just go for foods, but also for clothing. So humans have selected for cotton with long lint. And that served as a basis for clothing and sort of allowing us to have fabric. And I just want to end with a little story about the almond, which is part of the archaeological evidence for when almonds were domesticated was when King Tut's tomb was unearthed. And they found a pile of almonds next to the tomb, because the Egyptian culture, what they did is they buried the dead with food to sustain them in the afterlife. So that just gives you an idea as to how far back the importance of genetics goes.

If we think about nowadays, right now you are always seeing genetics in the news. And you also have the opportunity yourself to sort of do your own genetic experiment. And so now you guys are undoubtedly aware of all these companies that want you to send them your DNA. And they also want you to send them money, such that they can give you information about your family tree and also information about your health.

So this is now a big business. But if you don't understand genetics, this is not as useful as it could be. So I'm just curious. How many people here have used one of these services and had their DNA genotyped? Cool. And do you think that really changed your view of who you are? Or was it kind of, eh?

AUDIENCE: We actually-- I don't know if we even looked at where we came from. We looked for genetic disease.

ADAM MARTIN: So you're looking for genetic disorders. And you don't have to tell me anything about that. Yeah, so I have not done this, but my dad has done it. And he will go find his relatives and bore them with our ancestry. So this is one example of how genetics is really in play today. And not everyone knows how this works. I've had people at Starbucks in the morning come up to me with their 23andMe profile and ask me to explain stuff, because they know who I am. It's a little awkward.

So we can also use genetics for forensics. And so this is kind of a-- I had a lab manager in the lab, and he told me that people were doing this in senior homes in Florida, which I thought was kind of funny. What I find hilarious about this is the mug shot of the dog. That dog looks so guilty. But you can use DNA to-- you can use DNA to genotype poop. You can genotype your neighbor's dog. You can get evidence that they're the one that's pooping on your lawn. So that's a not-so-serious example.

But there are more serious examples of where DNA genotyping is really having an effect in our society. And this is something I mentioned in the intro lecture. Just this past spring, someone was suspected as being the Golden State Killer. This is a cold case. The killings happened 40 years ago, but the break came from investigators getting DNA from the suspect's relatives to implicate this person in this crime. So they had DNA from the crime. And they saw that there were matches to the DNA at the crime to certain people. And then they can reconstruct who might be the person in the right place to commit the crime.

So this is-- I think this is interesting, because it also leads to all sorts of privacy issues, right? Who's going to gain access to your genotype if you submitted to these companies, right? I mean, this is probably a case where I'd argue there's probably a beneficial result in that you can actually figure out if someone's committed a crime. But there are other issues in terms of thinking about insurance companies where we might be interested in having our information not publicly available to insurance companies. And maybe this is something we can discuss later on in another lecture.

For today, I want to move on and go through really the fundamentals of genetics. And what I'm going to do is I'm going to start with the answer. OK? I'm going to present to you guys today the physical model for how inheritance happens. OK? So today, we're going to go over the physical model of inheritance.

And this physical model involves cell division, which you saw in the last lecture and also in my opening slide. It involves cell division and the physical segregation of the chromosomes during cell division. So also chromosome segregation.

OK, so this is how I'm going to represent chromosomes. And I just want to step you through what it all means. So I have these two arms that are attached to this central circle. The circle is meant to represent the centromere. So this is the centromere.

And you'll remember from the last lecture on Monday, the centromere is the piece of the chromosome that physically is attached to the microtubules that are going to pull the chromosomes to separate poles. OK? So that's called the centromere. And usually, it's denoted, it's like a constriction in the chromosome or a little circle. OK?

These other parts of the chromosome are the chromosome. So that you have the arms of the chromosome. Now I'm drawing what's known as a metacentric chromosome. It's not important that you know that term. But it just means that the centromere is in the middle of the chromosome. There are other types of chromosomes with the centromere might be at the end. OK? So there are different types of chromosomes.

All right, now, for all of us, we have cells that have different numbers of chromosomes. OK? Some of our cells are what is known as haploid. And what I mean by haploid is there is a single set of chromosomes. Now the cells that we have that are haploid are our gametes, so they're our eggs and our sperm cells. OK? So these include gametes.

OK, but most of the cells in your body are what is known as diploid. And diploid means there's two complete sets of chromosomes. OK, and you get one set from one parent, the other set from the other parent. OK? So one set from each parent.

OK, and I'll draw the other set like this. And what I'll do is I'll just shade in this one to denote that it's different. OK? So these two chromosomes then are what is known as homologous. They're homologous chromosomes. Homologous.

OK, and what I mean by them being homologous is that, basically, these two chromosomes have the same set of genes. OK, so they have the same genes. They have the same genes. But they have different variants of those genes. OK, so different variants of these genes. And these variants are referred to as alleles. OK? So if you have the same gene but they differ slightly in their nucleic acid sequence, then they're distinct alleles of those genes.

So often, the way geneticists refer to these different variants or alleles is we use a capital letter and a lower case letter. OK, so this chromosome over here might have a gene that's allele capital a. And then this homologous chromosome will have the same gene but a different allele, which I'll denote lowercase a. OK?

So in this case, big A and little a are different alleles of the same gene. They might produce a slightly different protein, which would result possibly in a different phenotype. OK? So everyone understand that distinction?

Oh, I want to make one point because this came up last semester and was one of those cases where I forgot the part about the head. So we often just have two alleles when we teach genetics. But I hope you can see that because a gene is a long sequence of DNA, there is a ton of different alleles you can have within a given gene. So one nucleotide difference in that gene would result in a different allele. OK? So we often refer to two alleles, but there can be more than two alleles for a given gene. OK? Does everyone see how that manifests itself? OK, great. Any questions up until now? Yes, Carmen?

AUDIENCE: So when you say that there's more than one, more than just the two alleles, I don't have more than one on each chromosome. So they're just more than one--

ADAM MARTIN: In the population. So Carmen asked, well, can I have like five alleles of a gene? And that's a great question. And so thank you, Carmen, for asking that. What I mean is if we consider a population as a whole, right?

You have two alleles of each gene, unless it's a gene that somehow duplicated. And so when we're considering the population, there can be more than-- right? I mean, I see we have people with-- hair color is not a monogenic trait. But we have people with black hair, with blond hair, with brown hair, right? There is more than just two possible alleles with possible phenotypes. OK?

All right, let's go up with this. All right, now I want to start at the beginning. So most of our cells are diploid. And the origin of our first diploid cell is from the union of two gametes. OK? So I'm going to draw two gametes here. Each is one n.

And I'm just going to draw one set of chromosomes for this here. So we might have a male gamete and a female gamete. And what I'm referring to when I say n here, n is basically referring to the number of chromosomes per haploid genome. So when you have one n, it means you're haploid because you have only one set of haploid genome.

But early in your life, we're all the result of a fusion between a male and female gamete. And so that creates a diploid cell. OK, so now, this diploid zygote, so this is referred to as the zygote, is diploid and now has a set of homologous chromosomes. OK? So I'm only drawing one set of homologous chromosomes here.

So on the board, I'm going to stick to just one, so I don't have to draw them all out. In the slides, I have three. OK? So each of these represents a chromosome. These are different chromosomes. Different chromosomes are either different color or have a different centromere position. And then these down here that are colored are going to be the homologous chromosomes. OK? Do you see how I'm representing this?

OK, so once you have the zygote, right, so you guys are no longer one cell, right? You guys each are tens of trillions of cells. So this zygote cell had to reproduce itself, and your cells had to divide, so that you grew into an entire multicellular organism. I'll just quickly erase that.

OK, so when most of your cells divide, and most of your cells are known as somatic cells. When cells of your body or your intestine and your skin, when they divide, they genetically replicate themselves. And they're undergoing a type of cell division known as mitosis. OK?

In mitosis, it's essentially a cloning of a cell. Or ideally, it's the cloning of a cell. So you have a diploid cell. It has to undergo DNA replication . And when a chromosome undergoes DNA replication, it will, during mitosis look like this. OK?

And these two different arms or strands, they're known as sister chromatids. OK? So that's just another term you should know. These are sister chromatids. OK, and the sister chromatids, if DNA replication happens without any errors, should be exactly the same as each other in terms of nucleotide sequence. OK?

So after DNA replication, this cell will essentially have four times the amount of DNA as a haploid cell. And it will split into two cells. And again, they'll both be diploid. OK? And I'll just point out, if we're thinking about our pair of chromosomes here, right, this parent cell has both homologs. And the daughter cells, because they should be genetically identical, also have both homologs.

OK, so that's an example with just one chromosome. I'll take you through an example with these three chromosomes here-- all six chromosomes. So you have-- these are homologs. These are homologs. These are homologs. And during mitosis, all of these chromosomes initially are all over the nucleus.

But during mitosis, they will align along the equator of the cell and what is known as the metaphase plate. Metaphase is just a fancy term for one particular stage in the mitotic cycle. And then what will happen is the spindle will attach to either one side or the other side of these chromosomes.

And it will physically segregate them into different cells, OK? And what I hope you see here is that this has six chromosomes. This has six chromosomes. And these two daughter cells are genetically identical to the parent cell. OK, so this is known as an equational division, because it's totally equal. OK?

And again, the daughter cells are both diploid, OK? So that's mitosis. Any questions about mitosis? OK. Moving on, we're going to talk now about another type of cell. And these are your germ cells. And these germ cells undergo an alternative form of cell division known as meiosis, OK? And your germ cells-- germ cells produce your egg and sperm.

And so meiosis essentially is producing gametes, such as egg and sperm cells, OK? So what's the final product going to be? What should be the genomic content of the final product of meiosis? It should be one end, right? Who said that? Sorry. Yeah, exactly right. What's your name?

ADAM MARTIN: Jeremy. So Jeremy is exactly right. Right? The germ cells-- in order to reproduce sexually, they should be haploid cells, so that they can combine with another haploid to give rise to a diploid, OK? So the ultimate result that we want is to have cells that are one end.

But most of our cells to start out with are diploid, so they're two end, OK? So what's special about meiosis is you're not just going from two end to two end, but you're reducing the genetic content of the cells. You're going from two end to a one end content, OK?

So again, meiosis starts with DNA replication. But in this case, the first division, which is meiosis I, is not equal. And it actually segregates the homologs, such that you get one cell that has one of the homologs duplicated and another cell that has the other homolog duplicated. OK?

And I'll show this. I'll show it right now. So this is the same cell now. It's undergone DNA replication. As you can see, each chromosome has two copies. But instead of all the chromosomes lining up in the same position of the metaphase plate, what you see is that homologous chromosomes pair at the metaphase plate.

And what happens here is that the homologous chromosomes are separated-- two different cells. And now, you have two cells that are not genetically identical, OK? So because there is not equational and there's a reduction in the genetic material that's present in the cells, this is known as a reductional division, OK?

So that's meiosis I. And that's a reductional division. And then-- but this is not yet haploid. And so-- here, I'll just stick another one in here. These cells then undergo another round of division, which is known as meiosis II. And during this meiosis, these sister chromatids are separated, such that you're left with one chromosome.

And my drawing-- at least one chromosome per gamete, OK? So each of these, then, is 1n. OK? So again, you have the chromosomes. But this time, you have them aligned like in mitosis. They align. The sister chromatids are physically separated.

And now, you see this cell is genetically identical to this cell. And this cell here is genetically identical to this cell, OK? So that's meiosis II. And that's an equational division much more like mitosis, OK? Because the product of the division of those two cells-- each of those is equal, OK?

And finally, the result of meiosis II is that you're then left with gametes that have a haploid content of their genome. OK, I want to end lecture by doing a demonstration. Let's see. So this could either be amazing, or it will be a complete disaster. So we're totally going to do it. So everyone come up. Right here. Here.

Evelyn, you can leave when you have to go. And we'll have a chromosome loss event. OK? It has to be a multiple of four. If we have extra people label, then the people can supervise. Go. Oops, sorry. All right. What do we got here? Here you go, Bret, Andrew. Sorry. I hope I'm not hitting anybody.

ADAM MARTIN: What's that? Yeah, that's the advantage of these. All right. Here you go, Myles. Let's see. Here you go. Sorry. Someone take this. All right. What do we got here? Just got a little chromosome here.

ADAM MARTIN: Oops, sorry. All right. Who doesn't have a chromosome? Everyone in the class has a chromosome? All right. One of you want to come in here? All right. We'll see how constrained we are in terms of space.

I've never been this ambitious and had this many chromosomes before, so I'm excited to see how this works. So you each have a Swim Noodle. They're different colors, so different colors represent different chromosomes. And then you also have Swim Noodles that have tape on them.

And these represent different alleles from your other chromosomes. So these two chromosomes would be homologs of each other, OK? Does that make sense? OK, great. All right. Now, the metaphase plate will be along the center of the room.

So let's first reenact mitosis. So why don't you guys find your sister chromatid and then sort of align in the middle of the room here? Sister or brother chromatid. How are we doing? Do we have enough space there? It's a little packed. You can see how the cell-- can you imagine how packed it is inside a cell?

OK, everyone found their sister chromatid. Normally, the sister chromatids-- they replicate and they get held together. So there's no finding of sister chromatids, but-- all right. Great. So segregate and we'll see how you guys did. All right. And the goal is that you guys would be genetically identical. So how-- OK, great.

That looks like one short red, one short red. OK, that's good. They look genetically identical to me. All right. So that was my mitosis. Now, we're going to do meiosis. OK, why don't you guys align, like what would happen during meiosis I. OK, you guys can come back. Think about who you're going to pair with.

All right. So what were you looking for when you were pairing? Who were you looking for?

AUDIENCE: Longest chromosome.

ADAM MARTIN: Your longest chromosome, right? OK, great. All right. Why don't you guys segregate? All right, so that was meiosis I. Meiosis I looks successful to me. And now, we have to undergo meiosis II. So maybe what we could do is you guys can rotate. And the metaphase spindle can be sort of in this orientation.

ADAM MARTIN: Yeah, that will-- we want a group over there, a group over there, a group here, a group here. And those will be our four gametes.

All right. You guys set? All right. Go.

OK, terrific. Everyone haploid? Looks like everyone is haploid, which is good. Right? So let's just take a minute and think about probability here. So what was the probability that a gamete would end up with this orange allele on the red chromosome?

ADAM MARTIN: Half, right? Because there are two, right? So these two gametes have that allele. These two should not, right? OK, great. And we just had a chromosome loss, so that gamete is in trouble. But maybe we could get a TA to rescue this chromosome. Either one of you is fine. There you go, David.

All right. That was great. Now, let's-- as you're doing this, you get a sense as to how things could get mixed up, right? And you think inside the cell, right? So I don't-- I've lost track of how many chromosomes. We have 1, 2, 3, 4, 5, 6, right? How many chromosomes do we have?

ADAM MARTIN: We are-- a haploid set for us is how many chromosomes?

ADAM MARTIN: 23. Exactly. Right? So it'd be even worse for a human cell to get this to go right. So why don't you guys line up in the mitosis configuration? And we'll consider some things that could go wrong. All right. Who here is good friends with their sister or brother chromatid? Is anyone very good friends with their sister or brother chromatid?

ADAM MARTIN: Yeah. Someone become good friends and become inseparable, OK? Would someone volunteer to be inseparable? OK, great. You guys are now inseparable, OK? Now, segregate. OK, great. Now, what happened there?

ADAM MARTIN: Yeah, that's cell stole her. OK. So now, we have two-- a duplication of that chromosome. What's happened over here with this daughter cell?

AUDIENCE: It's missing a chromosome.

ADAM MARTIN: It's missing a chromosome, right?

ADAM MARTIN: So these are the types of mistakes that can be associated with a cell becoming cancerous, right? Because let's say there was a gene that suppresses growth on that chromosome. And it wasn't on that homolog. Then you might result in a genetic sort of mutant or loss of that gene that would result in uncontrolled proliferation.

Also, picking up the extra copies of genes that promote growth could allow that cell to have a proliferative advantage, OK? We're going to-- this is sort of foreshadowing what we're going to talk about later. But I just want to plant the seed now. OK. Why don't we go back and do meiosis?

OK. Now, anyone see any friends looking across the aisle now? All right. Great. You guys are now inseparable. Why don't you guys segregate, except the inseparable ones? Oh, but your sister chromatids still have to stay attached. There you go. See? Great. Right. So just like last time, this is known as a non-disjunction event where the chromosomes don't separate when they should, OK? Great. Now, why don't you guys do meiosis II?

All right. You can segregate. All right. Now, you see these two gametes over here are lacking an entire orange chromosome. And these two gametes here have picked up an additional copy of an orange chromosome, OK?

So these two gametes are no longer haploid for the orange chromosome. And if one of these gametes were to fuse with a haploid gamete that has an orange chromosome, then now you have a zygote that has three copies of the orange chromosome, which is abnormal, OK?

So if that were chromosome 21 in humans, that would result in something that's called trisomy 21, which is down syndrome, OK? So you see how mistakes in how chromosomes segregate can result in human disease. OK. Why don't we give yourselves a hand? Good job.

OK, you can just throw the Pool Noodles on the side. And I just have one slide to show you where we're going next. [INAUDIBLE]

AUDIENCE: So I have a question.

AUDIENCE: When the homologous chromosomes split, can you share alleles? Are there alleles preserved in this portion?

ADAM MARTIN: You're asking if there's crossing over?

ADAM MARTIN: There is crossing over. Yes. And that will get its own entire lecture. Yes, good question. OK, so just to give you guys a preview of what's up next. So in the next lecture, we're going to talk about Mendel and Mendel's peas. And we'll talk about the laws of inheritance, OK?

And realize Mendel was way before DNA or what our knowledge of a gene was, OK? Next, we'll talk about fruit flies, and Thomas Hunt Morgan, and seminal work that led to the chromosome model of inheritance and also resulted in the concepts of linkage and also genetic maps.

OK, we're going to go-- well, just to sort of anchor yourself, the structure of DNA was published in 1953. So these seminal genetic studies up here were done before we knew about DNA. So geneticists were studying genes and their behavior well before we knew DNA was what was responsible.

And then we'll talk about sequencing and the sequencing revolution. We'll talk about cloning, and molecular biology, and how one might go from a human disease to a specific gene that causes it. And then, finally, we'll start talking about entire human genome and genome sequences. OK, so that's just a preview of where we're going, so have a great weekend.

Watch the video: Πιπεριές από σπόρο. (May 2022).