Genetics of Cinnamon

Summary:
Cinnamon - sex-linked recessive
Normal - dominant

Cinnamon is a sex-linked mutation. This means that the gene is located on the x-chromosome. Male budgies have two x-chromosomes (XX) and female budgies have an x-chromosome and a y-chromosome (XY). Since the gene is recessive to normal, male budgies must have two cinnamon genes (one on each x-chromosome) to be a cinnamon variety. However, since female budgies have only one x-chromosome, if their x-chromosome has the cinnamon gene, they will be the cinnamon variety. It is because females need only one gene to express the trait that sex-linked mutations such as cinnamon are more common in female budgies. Here, we will represent the cinnamon gene on the x-chromosome as "X^c" and the x-chromosome with the normal gene as "X". There are three genotype possibilities for a male budgie:

• XX - Two normal genes resulting in a normal male budgie.
• XX^c - One normal gene and one cinnamon gene resulting in a normal male budgie that is split for cinnamon.
• X^cX^c - Two cinnamon genes resulting in a cinnamon male budgie.

And there are two genotype possibilities for a female budgie:

• XY - A normal gene resulting in a normal female budgie.
• X^cY - A cinnamon gene resulting in a cinnamon female budgie.

Below are some punnet square examples of pairings. As you will see, if your goal is to breed a sex-linked mutation like cinnamon, besides breeding two visually cinnamon budgies, the best results will be from the pairing of a male who is split for cinnamon to a cinnamon female.