These are the two chicks I got out of it, they don't have names yet...
Cochin Brahma cross
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If both parents carry the proper genetics for their breeds correct comb, I believe you will get all pea combs of some sort on both sexes.
In that case the "Brahma" parent did not carry two copies of pea comb as a pure bred Brahma would.
Pea comb is dominant over single comb. A bird with a single copy of pea comb will still have some form of pea comb, but only half of it's chicks will receive the pea comb gene. The other half could be single combed, depending on the genetics covered by the dominant pea comb, and the genetics of the other parent.
Nope. To my understanding single comb only occurs in the absence of pea, rose, or other dominant comb types.
Breeding two single comb birds should produce only single combed chicks because if there where any other genes present they would have shown in the parents. Now I imagine there are all kinds of modifiers that can alter the size and shape of single combs. Such as the difference between the single combs on a Cochin verses a Leghorn.
Same deal, your rose comb was not carrying two copies of rose comb.