egg color

In terms of brown egg shell color it is polygenic. This just means that there are a lot of genes that affect the trait. You can only breed the best to the best and hope for the best. The problem with sex-limited traits like egg shell color is that you can't select males for the trait. A male could have hatched from a dark brown shelled egg, but may not have the genes needed for dark brown eggs. It depends on the genes he inherited from his father and mother and it is a crap shoot as to whether or not he got the genes that you want. The way industry gets around this problem is that they look at the males relatives and estimate the chance that he has the genes that they are looking for. The more relatives have the trait the more likely that male will carry the wanted genes. They also progeny test males and see how their daughters perform. This provides information that can be used to select the males sons and daughters. Most backyard breeders can't do this fancy genetic analysis so they are stuck with trial and error. If you pick the wrong male it can set your selection backwards. the smart thing to do is to have several males producing the next generations so that you may go backwards with some, but hopefully in a forward direction for most, just selecting on the basis of what their mothers did.

There are more genes that letters in the alphabet, so we use single letters when we can, but as more genes are described the symbols get longer. The mo stands for recessive mottling, and the F stands for dominant frizzle. Capitals for the dominant allele (alleles are variant copies of the same gene) and lower case letters for the recessive alleles. Sometimes people place a + symbol with the letters (usually superscript, but that is hard to do in this forum). A + symbol indicates the wild-type allele. For mottling the dominant allele Mo+ is the wild-type (found in junglefowl) and the mo allele is the mutant. For frizzle the dominant allele (F) is the mutant and the recessive allele (f+) is the wild-type.

Except for sex-linked genes all animals have two copies of every gene, so they can have two of the same or two different copies.

Dominant alleles are expressed over the recessive alleles, so an Ff+ bird is frizzle and an f+f+ bird is nonfrizzled. For mottling Mo+Mo+ and Mo+mo birds are not mottled, and momo birds are mottled.