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Rare Females

Mostly about humans, but might happen in other species, too
  [vote for,

I have an Idea regarding human genetics that is associated with an intriguing possibility. It is possible that something that I think I know on this subject is erroneous, which would render my Idea unBake-able by Nature. Therefore I need to explain what I think I know, in order that the esteemed members of this site might point out any flaws --but also to explain why the Idea might make sense.

Thanks in advance for your patience in wading through the following.

Sometimes an ovum is constructed that contains no nuclear DNA of its own. If a sperm containing a Y chromosome merges with that ovum, the first thing that happens is, all the DNA in the sperm gets duplicated, so that every chromosome becomes part of a pair.

However, a zygote with a YY chromosome pair is not viable, and leads to a medical condition known as a "molar pregnancy", involving a thing called a "hydatidiform mole". Such a pregnancy must be terminated lest it cause "trophoblastic disease".

But what if the sperm had an X chromosome instead? In that case the initial duplication process should yield an XX pair for the zygote, which has a chance of being viable, forming a normal female body.

I fully understand that in such a case every single genetic defect in all the chromosomes would be duplicated and result in a matched defective gene-pair. An actual normal female body resulting from the preceding events might be extremely rare; the zygote might not actually ever be viable enough to ultimately yield even a living female body, much less a normal one.

Still, I find the possibility intriguing, that a few women might be walking around, each of whom doesn't have any of her mother's nuclear DNA (she will have her mother's mitochondrial DNA), but only has nuclear DNA from her father's mother. If she is normal, she must have a nearly defect-free gene chart!

Has anyone thought to look for that? Or found some evidence for it by accident?

Vernon, Feb 04 2016

Some data about molar pregnancies http://www.mayoclin...causes/con-20034413
This is how I concluded that the Y-chromosome got duplicated. No restrictions on duplication are mentioned. [Vernon, Feb 05 2016]

Mole cytogenetics http://www.ncbi.nlm...gov/pubmed/26535984
[bungston, Feb 05 2016]


       I've thought of one error, involving the fact that humans have 23 pairs of chromosomes, and when sperm are manufactured, the pairs are randomly broken up to obtain 23 individual chromosomes for 1 sperm. So some of that DNA comes from the father's mother, but also some of it can come from the father's father. The X chromosome itself is guaranteed to have come from the father's mother. But not the others.
Vernon, Feb 04 2016

       Just think what this means for any woman who thinks she has nothing in common with her mother! She might be more right than she knows!
Vernon, Feb 04 2016

       // However, a zygote with a YY chromosome pair is not viable, and leads to a medical condition known as a "molar pregnancy", involving a thing called a "hydatidiform mole". //   

       Source? Wikipedia's molar pregnancy article says "46,YY (diploid) is not observed."
notexactly, Feb 05 2016

       It's an interesting possibility. I work (partly) on IVF and chromosomal anomalies, and the number of weird things that can happen at the chromosome level is truly amazing.   

       I would wager that there are some people walking around with two copies of one of their chromosomes from the same parent. However, whether a full chromosome set from one parent would be viable is doubtful.   

       In particular, there are epigenetic factors - for many genes, one copy (either the paternal or maternal) is switched off while the other is on; a doubled-haploid individual would have this system all messed up. And, as you noted, any recessive disorders would manifest themselves - I suspect that haploid genomes with *no* lethal defects are incredibly rare.   

       Interesting, though.
MaxwellBuchanan, Feb 05 2016

       It looks like YY is not OK even for a mole. Which makes sense; a bunch of stuff is on X and only ear hair on Y. Moles are XX or, if 2 sperm team up, possilby XY.
bungston, Feb 05 2016

       I'm rather concerned that this idea is not so much half baked, as actually so perfectly baked that it produces buns of such unqualified loveliness that all men everywhere will fight to the death for them, resulting in total decimation of y- chromosomes, and consequent death of the entire human race. But then, some people reckon that might not be such a bad idea. So - carry on.
Notes, Dec 03 2017


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