Asexual Reproduction: Weed, Grass & Self-Fertilized Animals

[yan-cha]

Asexual reproduction does not give genetic variations and the offspring soon die out due to being unable to adapt themselves to changes of environment. But because they each time give birth to a big population and each of the children dies at different time, asexual reproduction still exists among weed, grass...

<I>Is such an assumption correct ? Please check that "verse" of mine...
<II>Second I would like to know how weed can give birth to other weed.
<III>And finally , why self-fertilized animals like some kind of fish are not considered asexual reproductive ones ?

Thanks a lot,

 

[gerben]

<I> Many plants that reproduce asexually also produce sexually. If they would only reproduce asexually and in no way exchange genes they would be prone to extinction. Variation in the lifetime of individual specimens is not important. The danger of extinction is because there would not be enough variation in such a species so that when the environment changes a bit there would be no variants that where adapted to the new environment and that would flourish at the expense of other variants that would diminish; they would all diminish until there is none left.

<II> Many different ways, for example by a branch or a leave falling of and growing out to full plant or a roots grow some distance horizontally and make part of it then bud into a new plant, after time the root connecting the two plants may break or rot.

<III> Because they produce two kinds of reproductive cells like egg cells and sperm cells, that both carry half of the genetic information from the fish. In a somewhat random way half of the genes are copied into egg cells and also in a somewhat random way half of the parents genes are copied into sperm cells. When an egg cell and a sperm cell are combined you end up with a different collection of genes than the parent had, because you can copy half of the parent’s genes in many ways.

 

[Moonbear]

If it involves fertilization of gametes, be it sperm and egg of animals or pollen and ovum of plants, it's considered sexual reproduction. It doesn't matter if it is self-fertilization or cross-fertilization.

I think gerben addressed everything else. Let us know if you need further explanation.

 

[nipwoni]

Actually, asexual organisms can be quite successful. Variation can be created in their genes by mutations. Sexual reproduction does not actually create variation, it just reshuffles genes to produce new combinations. The only way to introduce new variation is through mutation.
Some of the fastest-adapting species are asexual organisms, especially microbes. They tend to have short generation times, and some of them have genes that can be mutated more easily. For multicellular organisms, asexual reproduction tends to be less successful, maybe because of longer generation times. Some animals and plants have been able to get away with reproducing asexually though, even if they never reproduce sexually.

 

[bross7]

But you are more likely to accumulate deleterious mutations in asexual reproduction to the high rate of reproduction, and there is a lesser chance of being able to select against them as asexual reproduction would carry over any mutations (barring a new mutation occurring that managed to have a drastic effect (unlikely).