Quote Originally Posted by dr del View Post
Hi,

I was actually reading something about this a couple of days ago that mentioned several ways different genetics can exist in the same individual.

I may have misunderstood because it said every female human was a mosaic because only one of the x chromosomes is active in each cell and one of the xx pair comes from the father?

Also something about marmosets commonly having their brothers sperm!

Apparently chimerism isn't always a rare occurance and can sometimes even be more common than what we think of as "the norm" depending on the species etc.


dr del
Yup, all female mammals are mosaics at the X chromosome. One X chromosome gets kicked out of a stem cell early in development, and the other one does all "the work." That is, the genes from only one X chromosome are expressed in each cell.

Cats offer a nice visual example of this. In cats, genes for coat color are carried on the X chromosome. A calico cat gets black from the X chromosome from one parent and orange from the X chromosome from the other parent. Whether an area is pigmented as orange or black depends on which X chromosome was kicked out early in development. That's why calico cats are always female. (the white spots come from a different co-dominant gene)

Note: snakes are a bit different from mammals in that males are ZZ and females are ZW.