Forgive me if this has been asked already. This is an awsome service and resource, thank you for your time (and interest!)
Im very new to chickens and breeding/genes. I have a splash andalusian roo Id like to experimentally breed with a speckled sussex hen, wondering what sort of phenotypes could result?
For feather color:
All chicks should be blue, probably with some red or white leakage as they grow up.
Other traits: chicks should have a body type in between their parents (not as slender as Andalusians, but more slender than Sussex). Daughters' eggs will probably be cream or very light brown. Chicks should be like their parents in having single combs, no feathered legs, no feathered crests on their heads, no extra toes.
Daughters will probably have leg/foot color that is darker than what the sons have. They may look alike at hatch, but the darker color should develop within a few weeks on the females.
Genetic explanations for the feather color:
The Andalusian should give every chick the Extended Black gene (often referred to as E), which makes a chicken black all over. That gene is dominant over the genes that allow red-and-black patterning (like the Sussex has), so the chicks will all have a black base color.
The blue gene is incompletely dominant, and affects all black on the chicken. Your Splash rooster has two copies of the gene, turning all his black to splash. He will give one copy to each chick he sires, which will turn all their black into blue. So they will be "all black" (from E), turned into blue by the blue gene.
The speckles on the sussex are caused by the mottling gene. It is recessive, so you only see the effects when a chicken inherits it from both parents. Each chick will inherit the mottling gene from the Sussex parent, but not from the Andalusian parent, so they will carry mottling (can give the gene to their chicks) but not show it.
Leakage is fairly common with chickens that are otherwise all black or all white. It most commonly appears as red in the shoulders of males, and red or salmon color in the breasts of females, but it can also appear in other places or as other colors (such as white in a black chicken, or some shade of yellow). There are a number of genes that can work together to prevent it, and most purebred chickens have been strongly selected to have those genes, but it is quite common when you cross different colors of chickens with each other.
Foot color genes:
There is a dominant gene on the Z sex chromosome, that causes light skin. The Sussex hen should have this gene. The recessive form of the gene allows dark skin, and the Andalusian rooster should have this form. A rooster has sex chromosomes ZZ, so he gives his dark-foot gene to every chick he sires. A hen has sex chromosomes ZW, so she gives Z to her sons, with the dominant gene that causes them to have light feet. The hen gives a W chromosome to each daughter, which makes them female but has no effect on their foot color. That lets them show the dark skin they inherited from their father.
There is another gene that controls whether the feet have a yellow vs. white color. Both the Andalusian and the Sussex should have white, so the chicks should as well. For chicks that have dark skin, the white or yellow can usually be seen on the soles of the feet. The upper parts look slate/blue (for white skin) or willow/green (for dark skin.)
