Reciprocal cross.

[sillysmile]

could somebody please explain the point of a sex-linked reciprocal cross to me?

also what's the diff between Y-linked inheritance and sex-limited inheritance.
thanks beforehand.

[Russ]

Well I've never heard them called "sex linked" reciprocal crosses, but the purpose of this cross is to determine the mode of inheritance (or as wikipedia puts it "to test the role of parental sex on a given inheritance pattern"). Assuming you know the mechanics of the cross, the purpose is to determine whether or not the gene under investigation is sex linked. If you see different phenotype ratios between the offspring of the crosses, you can conclude that the gene is sex-linked. If the ratios are the same, the gene is autosomal.

Y-linked inheritance is pretty simple - the gene is located on the Y chromosome and is thus always passed down, father to son. The only way for a woman to be affected is for her to have a chromosomal imbalance or mutation. Sex-limited inheritance just means that the expression of the gene is affected by the sex of the offspring - for example, a woman could not be affected by a disease that caused testicular cancer (broadly speaking).

Don't confuse sex limited with sex linked!

[sillysmile]

yep, you make quite a bit more sense to me than my textbook. I think you are right about sex-linked reciprocal cross, I don't know where I got that term from. So basically, a reciprocal cross is used to determine whether a particular gene is sex linked or autosomal, pretty simple really. In regards to sex-limited inheritance: Could a gene that affects only the ovaries of a woman be an example?

[Russ]

Yes, that also works. It's worth noting, however, that it's not always that black and white. It's possible for both men and women to go bald, but the gene is still sex limited - in this case, the oestrogen produced by women acts to suppress the effects of the mutation.