How does parthenogenesis happen, specifically in sharks/rays?
In: Biology
The basic idea is, you have two sets of chromosomes. A specific pair of these chromosomes typically defines biological sex–in mammals, they’re X and Y (birds have Z and W, where its the female with both ZW, for example). But I’ll use XY for this explanation as a general theme.
During sexual reproduction, your cells (XX or XY) split these chromosomes, create a sex-cell of sorts (sperm/egg/whatever) that only has a half set, then pair with your partner’s to create a new complete set. If you are XX (biological female), you are contributing one of two X’s.
However, there are cases where either two of these cells with a halfset can recombine, thus giving you “complete” set that can result in a new generation, or this split is disrupted and you just… keep it all and proceed anyways. Thus, you can have birth without fertilization or a partner. However, this tends to be more advantageous / *possible* for some species than others, especially since it occurring through random disruption/error would need to ensure that *all* chromosome pairs don’t get separated. To my knowledge when it happens stably/consistently, it’s usually a fusion situation between halfset-containing cells.
This does however mean that, each generation produced through parthenogenesis tends to have very little comparative genetic variation, since it’s essentially self-cloning with maybe some added shuffling.
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