Genetics of Dark Factor

Summary:
Dark factor - semi-dominant
Normal - recessive

There are only two alleles that determine the darkness of a budgies body color: the normal gene and the dark factor gene. The dark factor gene is semi-dominant to the recessive normal gene. This means that a budgie that has one dark factor and one normal gene looks different from a budgie that has two dark factor genes. Here, we will represent the dark factor gene as "D" and the normal gene as "d". Therefore there are three possible genetic combinations for any budgie:

• dd - Two normal genes (homozygous) resulting in a normal light colored budgie (light green or sky blue).
• Dd - One dark factor gene and one normal gene (heterozygous) resulting in a single dark factor budgie (dark green or cobalt).
• DD - Two dark factor genes (homozygous) resulting in a double dark factor budgie (olive or mauve).

As you can see, the darkness of a budgie occurs in degrees, depending on the number of dark factors present. Below are punnet squares of some (but not all) possible pairings.