When we talk about genetics we talk about the genetic makeup that a bird consists of and what I mean by genetic makeup is information being carried on the chromosomes on the different sets of chromosome pairs that birds have.
When we look at chromosomes we see that they consist of 4 arms that can carry genetic information all except for the Y sex-linked chromosome that has 3 arms to carry genetic information. Each chromosome is 1 of a set of 2 and all chromosomes rest in pairs.
How genetic information is inherited is straight forward 50% of the genetic information inherited is inherited from the the father and the other 50% is inherited from the mother, how the genes from the mother and the father combine determine the outcome of the offspring and a profound understanding of genetics can enable us as breeders to predict the probability of what the outcome will be.
Mutations occur in the wild and in captivity and all this means is that additional information has been added/removed from a birds chromosomes resulting in a change in phenotype (what is seen visually) or genotype (genetic composition).
Mutations reside on different sets of chromosomes and not all mutations effect color, when 1 or more different mutations rest on the same set of chromosomes on the exact same position (known as loci) we can say that those mutations are alleles of one another. Not all mutations that rest on the same chromosomes are alleles of one another as not all of the mutations rest on the same position on the same chromosome.
Mutations are categorized under two categories the first being autosomal and the other being sex-linked, and a sub categories under these categories are recessive, codominant and dominant.
The sex-linked chromosomes in birds are the inverse of that in mammals and the expression for a male is XX where as a female is expressed as XY.
The term we use to define the exchange of genetic information between chromosomes is cross-over, cross-over can displace and replace a mutation with new information and in some cases of double mutations split them from one another.
It is important to note that all of this takes place in the reproductive stages and birds will never undergo any of these changes in their lifetime.
If a mutation is autosomal we know that there are 2 X chromosomes involved when it comes to the inheritance of mutations, there are multiple sets of chromosomes where mutations can reside.
If a mutation is sex-linked we know that the X and the Y chromosomes that determine gender are involved, there is only one set of sex-linked chromosomes where mutations can reside. The Y chromosome does not seem to carry any color mutations and is dependent on the mutation that lands on the X chromosome.
When a mutation is recessive it means that both of the chromosomes in the pair must have the mutation present for the mutation to display.
When a mutation is codominant it means that only one of the chromosomes in the pair can carry the gene for us to notice that this mutation is present and a “double factored” version of this mutation would not be different to a “single factored” version of this mutation.
When a mutation is dominant it means that only one of the chromosomes in the pair can carry the gene for us to notice that this mutation is present, a “double factored” version of this mutation would be different/more impressive to a “single factored” version of this mutation.