Genetics of Base Color

Summary:
Yellow-base - dominant
White-base - recessive

There are only two alleles for a budgie's base color: yellow-based and white-based. The yellow-based allele is dominant to the recessive white-based allele. Here, we will represent the yellow-based gene as "B" and the white-based gene as "b". Therefore there are three possible genetic combinations for any budgie:

• BB - Two yellow-base genes (homozygous) resulting in a yellow-based budgie.
• Bb - One yellow-base gene and one white-base gene (heterozygous) resulting in a yellow-based budgie that is "split" for white-base.
• bb - Two white-base genes (homozygous) resulting in a white-based budgie.

As you can see, the only way that a budgie will be white-based is if both of it's genes are the recessive white-base. If the yellow-base gene accompanies the white-base gene, the budgie will be yellow-based because the yellow-base gene is dominant. Such a budgie is heterozygous and is said to be "split" for white-base, which means it carries the recessive gene, but does not show it because of the presence of the dominant gene. Breeding two yellow-based budgies who are split for white-base can result in white-based budgies. However, it is difficult to tell if a budgie is split for white-base. It is said that if there is blue in the feathers around the vent of a normal yellow-based budgie, it is split for white-base. Either knowing the varieties of the parents or selective breeding can reveal the genetics of a particular bird. Below are Punnet square examples of possible pairings.