I don't know whether this is the correct forum for my question so please indulge me if it is not.
My understanding (such as it is) of the inheritance of X and Y chromosomes from parents is as follows.
Females inherit one of their mother's two X chromosomes and their father's only X chromosome.
Males inherit the Y chromosome from their father, and one of their mother's two X chromosomes.
My question concerns recombination between the mother's two X chromosomes before one is passed on. Most references I have been able to find on the internet seem to say that, as with Chromosomes 1 - 22, recombination occurs between the mother's X chromosomes before one is passed on to a child. Some references, however, say that recombination MIGHT take place, but might not.
If recombination occurred between the X chromosome which my mother inherited from her mother and the X chromosome which she inherited from her father before she passed one of them on to me, and before she passed one on to my sister, then my sister and I should inevitably have some kind of partial match on the X chromosome.
When I did an X-DNA comparison on GedMatch I was surprised to find that there was no match on the X chromosome - even if I dropped the cM threshold to 3. For clarity I should point out that the results of our autosomnal DNA tests show unequivocally that we are full siblings.
Just to add to my confusion, both my sister and I have a partial X DNA match with our female maternal 1st cousin.
I don't see how this is possible unless there was no recombination before one of our mother's X chromosomes was passed to me and also no recombination before her other X chromosome was passed on to my sister.
Has anyone else found a similar result between full siblings, and does anyone know how frequently this occurs?
