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chazwomaq t1_ixmcfhr wrote

Reply to comment by MonitorPowerful5461 in What are the most "intelligent" asexually reproducing species? by yourmom815

Asexual reproduction is not incest at all. The problem with incest is that it can expose recessive homozygous combinations (e.g. from heterozygotic parents) that can be deleterious. But asexual reproduction won't do this as the offspring is the same as the parent.

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GeriatricZergling t1_ixmjoqg wrote

Sometimes it is. Parthenogenesis isn't always forming a perfect copy of the parent, but can also involve eggs fusing back together or duplication of the chromosomes during various stages of meiosis. Depending upon which stage this happens at, it can be equivalent to selfing, or equivalent to clonal reproduction (sort of).

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chazwomaq t1_ixmkrl1 wrote

Yes, fair enough. Parthenogenesis can be different.

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MonitorPowerful5461 t1_ixmcmqy wrote

Right. But then asexual reproduction doesn’t allow for evolution? Surely that’s a massive disadvantage

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contrariancarbon t1_ixmehqf wrote

It actually does allow for variation, but at a much slower rate. Asexual offspring will still experience transcription errors and other random mutations. Naturally this is less of an issue for organisms that reproduce at a high rate than it would be for complex organisms.

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chazwomaq t1_ixmlg6b wrote

Many species reproduce asexually - many plants, for example, or bacteria (although they can share DNA plasmids directly). Evolution happens just fine, as variation is supplied by mutation. Nevertheless, sexual reproduction is the norm.

In terms of selection, it is sexual reproduction that is a massive disadvantage. From the gene's eye point of view, sex involves a "two-fold cost". Essentially any given gene has only a 50% chance of being in an offspring, compared with 100% for asexual reproduction.

Something needs to overcome this two-fold cost, most probably the fact the sexual recombination allows discovery of fitter genotypes for disease resistance and host/parasite coevolution.

https://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction

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