I want to learn more about genetics/inheritance in dogs/Labs. I remember some discussion before about a male getting his Y chromosom from his dad and his X chromosom from his mom. I'm just trying to figure out if that means that the male's paternal grandmother's line (X chromosom that he never got) becomes irrelevant or what. If there any any books that discuss this, I'd appreciate if someone can point me to them.
Debbie Kay's book discusses this. Not everyone buys into it, but it is a good read.
Boys carry XY chromosomes and girls carry XX. So when looking to breed, the resulting girls in a litter will get one X chromosome from their mother and one from their sire's mother (the sire is XY so can only pass on his X chromosome). The resulting boys will be XY so will get their X chromosome from their mother and their Y from the sire. So the male's bitch line would be relevant if you are looking to produce a bitch puppy.
Having said that, IMO a strong bitch line is ALWAYS a desirable thing behind a dog. The dog not only needs to be strong but he needs strong bitches behind him. The strength is always in the bitches and since most of us look to produce a nice bitch in a breeding, her theory makes very good sense 8)
To err is human:To forgive, canine."
Tatyana - ah, the famous "black holes" in pedigrees! Before jumping headlong into assumptions, we must be aware that the theory only pertains to sex-linked traits. We know of a few sex-linked traits in humans and in horses and can logically suppose they also exist in dogs, but I'm not aware of any study that pinpoints them. Dana already explained the basics, so I'll add to the confusion.
HYPOTHESIS: let's say that light eyes is sex-linked and is carried by the dogs on their Y chromosome - pure speculation. If your stud dog Bonzo has light eyes, then he inherited them from his sire, since his dam only gave him his X chromosome. It follows that Bonzo cannot transmit this trait to his daughters, since they have all received only his X chromosome. It also follows that his daughters' progeny will not inherit Bonzo's light eyes - the trait has therefore been eliminated. Bonzo's sons will have light eyes, since they inherited his Y chromosome with its baggage.
If you admire the bitch line of a particular stud dog, it could pay to be aware that he will not transmit any sex-linked traits from his dam to his male offspring. Since he will only be contributing his Y chromosome (inherited from his sire) to his male progeny, only the bitches in the litter will inherit sex-linked traits from their paternal grand-dam.
In a nutshell, when studying a dog's pedigree, his sire's dam is a “black hole” - that whole section of his pedigree cannot contribute any sex-linked traits. Likewise, when studying a bitch's pedigree, her sire's sire would be a “black hole”. Of course, many more genes get lost in any combination - we don't know which X chromosome a bitch transmits to her offspring (the one inherited from her sire or the one from her dam) but the black holes are a certainty.
Breeders have known for a long time now that the bottom line of any pedigree is of prime importance. Maybe because there are never any “black holes” in that area?!
Thanks, Dana and JP. Fascinating stuff. I'll look into buying Debbie Kay's book and learning more.