Originally Posted by junebuggena
Originally Posted by Ridgerunner
June that only works when you cross a chocolate rooster with a black hen. Chocolate is a recessive gene that modifies black. If you cross chocolate with chocolate, you get chocolate.
A chocolate rooster has two copies of chocolate and will give one to each of his offspring. A black hen has only one gene there and if it is “not-chocolate” it defaults to black. But the hen will only give a “not-chocolate” to her boys, she gives nothing to her girls. So the girls only get a chocolate from the father and will be chocolate. But the boys get a dominant “not-chocolate” from their mother and a recessive chocolate from their father. The dominant gene wins out and the males are black.
The way I understand, is that hens only need one copy of the chocolate gene to express and males need two copies. It's possible to have two chocolate parents produce non-chocolate, male offspring.
June, it is a sex linked gene. That means the hen only has one copy of it. She gives a copy to her sons and nothing to her daughters. Let’s use ch for the recessive chocolate gene and Ch for the dominant not-chocolate gene.
For a male to be colored chocolate, he has to have both copies at that gene pair to be chocolate. He has to have ch-ch. If the rooster is CH-ch or CH-CH he will be black, not chocolate.
Since a hen only has one gene at that location, not a gene pair, for her to be chocolate she has to have ch-. If she is not-chocolate she has Ch-, the dominant form, and will not be chocolate.
So a rooster that is chocolate has to give one of his ch to his offspring. He doesn’t have any non-chocolate CH to give. His sons and his daughters will get a ch. If the hen is also chocolate she gives a ch to her sons so all males wind up ch-ch and will be chocolate. But she gives nothing to her daughters so all the daughters have is a ch from their father so they will be chocolate.
So if the hen is ch and the rooster is ch-ch, both will be chocolate and all offspring will be chocolate. There is no dominant CH non-chocolate to cause a black chicken.
I think the reason you misunderstand this is that you are thinking the hen has a gene pair at that location. She doesn’t, she only has one gene, just like she only has either one red/gold or one barred/notbarred at those locations. That’s what makes them sex-linked genes. She does not have two.