genders and genetics

Question
I have been breeding rex rabbits for one year now, my problem is that I get more male kits then female (about 80% ). Is this genetic from one of the parents or is this just nature. I would love to hear your opinion on this. Thank you

Answer
Dear Marjie,

It's impossible to say why you are getting such a high proportion of males without more information.  Getting 80% males is not outside the realm of probability, though this percentage should decrease with a larger sample size unless something weird is going on, genetically.

It's possible, though not highly likely, that the female babies have a greater likelihood of inheriting a harmful allele of a particular gene that's on the X chromosome than the males.  This is possible in the case of an X-linked dominant allele, but this should be expressed by the parent carrying it unless s/he has a genetic "hot spot" on that gene that is constantly mutating during formation of eggs or sperm.

How big is your sample size?  Are the litters small, in general?  If so, then it's possible that males are also inheriting the X-linked dominant, but they are not viable, either.  

In human families, some people are predisposed to having sons or daughters.  Again, this could just be a matter of probability.  But we've all heard of some families in which "sons run in the family" (or daughters).  In such cases, it is possible that the female reproductive tract is somehow more hospitable to sperm carrying a Y chromosome (which are smaller and faster) or to an X chromosome (which are heavier, but last longer than X-carrying sperm).  

There are a LOT of possibilities here, not least of them simple chance.  But the most important information I can share with you about breeding is here:

http://www.bio.miami.edu/hare/breeding.html

I hope this helps.

Dana