Dominant genes. I don't think of them as the only thing that gets passed on, rather, I think of them as something that trumps everything else. I wonder though. Remember the rhode island red bantams that got hatched out last October (I think it was). I think there were 6 or 7 of them. The daddy was a rose comb and the mama a single comb. I expected the rose comb to trump the single comb and at least 90% of the offspring would have rose combs. Sounds dominant, right? I suppose if we had hatched 100 chicks out of that cross, there may have been 90 with rose combs but as it was, with 6 chicks, one had a rose comb.
So... I'm as lost as ever on this dominant gene thing.
When you are talking genetics, "dominance" only counts in expression, not inheritance. The offspring of an animal that has inherited one copy of a dominant gene, and one of a recessive gene, have an equal chance of inheriting either gene. In the case of the blue vs. white egg color, for example. Blue (O) is dominant over white (o). In a bird that has one copy of each gene, (Oo), each chick has a 50/50 chance of inheriting the gene for blue eggs. It's pretty much like flipping a coin. Now, if you were to toss that coin only 6 times, you
might get 3 "heads" and 3 "tails," but you could get 2 and 4, or 1 and 5, or even 0 and 6, and it wouldn't be "statistically significant" because your sample group was so small. The same is true of genetics. If you hatched 1000 chicks, roughly half would inherit the blue shell gene from the parent, and the other half would have gotten the white shell gene. But in a group as small as one clutch, the numbers could go any way, and it really doesn't mean anything.
And to make things really confusing, not all dominant genes are created equal. Some are completely dominant, and there is no obvious difference between individuals that have one copy of the dominant gene and one copy of the recessive, and those that have two copies of the dominant gene. Some, however, show a cumulative effect. The Blue/Black/Splash color gene is an example of this. The gene that causes the blue coloration is dominant - if a bird inherits it, the color of the feathers will be affected. A bird with two copies of the black gene, and (obviously) no copies of the blue gene, is black in color. A bird with one copy of the blue gene, and one of the black gene, is blue. A bird with two copies of the blue gene is splash, which is pretty much a white bird with a little bit of blue/black color scattered here and there in its feathers. Breed a splash to a black, and you will get all blues, but breed two blues together, and you get blue, black and splash.
In the case of rose vs. single comb, rose comb is dominant. Any chick that inherits the rose comb gene will have a rose comb. Clearly, your rooster has one copy of the gene for rose comb, and one for a straight comb, if he is throwing straight combed offspring. Interestingly, a rooster that has two copies of the rose comb gene has reduced sperm motility, meaning he may not be as fertile as one with a rose comb that also has a copy of the straight-comb gene.
