self pollinating plants.

[shyan]

this is something that has been bothering me for a bit, i tried to ask my instructor to explain it to me, but i guess he didnt understand my question.

in plants, like mendel's peas, where each induvidual organism only pollinates, and therefore, reproduces with itself, how is it that the species is maintained? it seems to me that since there is no mixing of the genes, each and every induvidual line of plants should eventually spawn a different species than its neighbor. or am i missing something?

[JDavidE]

Self pollinating plants have no genetic means of variation, they must breed true and be identical to the parent. Neighbouring plants, receiving pollen from different plants, will reflect variation.

A problem with self-pollination is that inevitable genetic errors are transferred to the succeeding generation and magnified. Those plants eventually weaken and fail to compete.

[mith]

Perhaps your question is, how can asexual members of a species share genes within the species?

[shyan]

yeah thats it. so are these species just doomed to extinction then? so why would they become asexual in the first place?

[Darby]

You're confusing asexual reproduction with self-fertilization. When sex cells are produced and the remixed in a single individual, they still produce varied offspring (moreso depending upon how many chromosomes there are - I wonder if there is a correlation between chromosome numbers in plants, which can be quite high, and tendency to self-fertilize-?), which self-fertilize and mix up the alleles again.

And just because an organism can self-fertilize doesn't mean that's all it does. If peas could only self-fertilize, they would have been lousy subjects for Mendel's crossing experiments...

[Darby]

Oh, and I should have mentioned that an ability to self-fertilize is a great adaptation in plants that can disperse widely - individuals often wide up all by themselves.

That's also why it's common in a lot of internal parasites.

[shyan]

i wish i knew how to word this T_T ok, asexual being A, and asexual being B, are supposedly in the same species. if they did mate with one another, they could produce fertile offspring. but since A and B, and C, D, E and so forth do not interbreed with one another, how is it that they manage to stay in the same species? if there is no gene flow throughout the population, shouldn't they all spawn a different species, or die off?

i think that is what im trying to ask....

[Darby]

Asexual species aren't defined the same way that sexual ones are, and that's what is confusing you. Asexual species share ancestry which gives them the majority of their genome. If there is enough variation, from mutations are lateral transfers and such, along any descendant line, then you might have a new species. But there doesn't seem to be much consensus about how much drift produces new strains and how much is needed to make new species.

Don't forget that such terms are just conveniences for us - they don't really exist as clearly in nature as we want for our own labeling purposes.