First, we need to review some basics genetics-- male is an XY and a female is an XX. No need to get more complicated. Please remember, a male will only inherit the Y gene from his sire, while his litter mate sister will only inherit the X gene from the sire's dam that the sire inherited. The litter Dam has two (2) Xs--which each and every puppy will inherit one (1) X gene. This is one of the reason while litter brothers will look widely different--they both have the same Y gene from their sire , but received different X genes from their mother. Same with litter sisters, they both receive the same X gene from their sire, but different X genes from their dam.
Sometimes one will hear, " Oh his sire was Ch.Big Whoopy Do's brother, so he's just as good." No, Sorry, he's not. Most likely he carries very different genes. Let's look at "black holes" and the odds of inheritance in a pedigree. Black holes in a pedigree are the dogs that have absolutely no influence on the overall dog produced.
Perhaps the easiest inheritance gene to understand is the Y gene in any male pedigree--the Y gene is directly linked and passed down all of the sires on the upper half of the pedigree--the sire, grand sire, great-grand sire and great-great-grand sire, and so forth. Thus for males, the Y gene path of inheritance is easily traced.
The X gene in the male pedigree is a bit trickier. The X genes will come from one of the two genes the Male's dam carried. One gene will be from the Dam's sire's maternal line (his dam), and one will be from her Dam--who would have inherited one of two genes from her dam, and the maternal gene from her sire. So, we have one of three possible genes! Not so easy to trace!!
Let's look at some pedigrees as an illustration. We will start with the male pedigree below of a litter I bred. The direct Y line is highlighted in Red; The X line in highlighted in Blue. The dogs not contributing to the pedigree are in Black--so one can see how it can happen that the well known dog in a pedigree is in a "black Hole" of the pedigree and has no contribution to the overall pedigree.
Cathy C. Arney