Going Without Sex
by MikeGene
One of the strongest candidates for ancient asexuals, bdelloid rotifers date back at least 40 million years. That's the age of the oldest bdelloid recovered from amber. Despite bdelloids' asexuality, they've diversified into 360 species.
[...]
For a molecular test, Meselson focused on four bdelloid genes. Sexual organisms inherit a copy of a gene from each parent. If two-parent reproduction vanishes, the organism just keeps copying its own genes. Like a fax of a fax of a fax, the genome gets glitches. If they aren't harmful, they build up. One copy of a gene in an ancient asexual can develop very different mistakes from the same organism's other copy. Without sex to spread them around, copies of the same gene within an organism can look as different from each other as if they began diverging when sex stopped.
That's what Welch and Meselson found when they checked genes in four bdelloid species.
August 30th, 2007 at 11:18 am
Hi Mike,
Maybe I got punched in the head one too many times. But could you help me understand the significance of this comment:
There is significance here that is escaping me. Shouldn't the disparity between the same pair of genes in an asexual organism be expected?
Thanks for any insight.
Comment by Doug — August 30, 2007 @ 11:18 am
August 30th, 2007 at 10:06 pm
Hi Doug,
IDiot that I am, I forgot to include the link to the above story (from 2000). Here it is.
Imagine we have two copies of gene A (a diploid organism). One copy acquires a mutation and we'll now call it gene a. If meiosis was occurring in a population of organisms, we'd expect to see not only Aa, but also AA and aa. In essence, they saw only Aa in this rotifer, leading them to hypothesize the creature is truly asexual. Anyway, that was 2000. The story is even more interesting now and I'll probably post about it later.
Comment by MikeGene — August 30, 2007 @ 10:06 pm
August 31st, 2007 at 9:25 am
Thanks for the link and the explanation.
Comment by Doug — August 31, 2007 @ 9:25 am