Dr John Pilkington answers questions on Genetics

Question to Dr John Pilkington from David Ennals

Since the Cinnamon Opaline variety is the result of the closeness of the Cinnamon gene and the Opaline gene on the X chromosome, and since Cinnamon Opaline cocks have two X chromosomes, they must be very rare, however, I have two Cinnamon Opaline hens.

Since both Cinnamon and Opaline genes are recessive, it is obvious that a visual (phenotype) Cinnamon Opaline cock must be homozygous for Cinnamon Opaline. You told me that you have two Cinnamon Opaline hens; it is possible to produce Opaline Cinnamon cocks as grandsons from both these hens. This is the breeding plan you should follow:

Mate a Cinnamon Opaline hen to either a Cinnamon cock or an Opaline cock. In the example I will use a Cinnamon cock.

Diagram 1

Shows how all offspring
will be Opaline and Cinnamon

As Diagram 1 shows, all the offspring will be phenotypically Cinnamon and also all the cocks will be split in their genotypes for opaline also.The reason that a phenotypical Cinnamon cock has been used is so that you do not "pollute" your Normals with the recessive sex-linked genes in future generations.

In the next mating, you will mate the Cinnamon cock (as per the bird in the box in Diagram 1) to a Cinnamon Opaline hen, this could be his own mother, your other Cinnamon Opaline hen or another Cinnamon Opaline hen.

Diagram 2

Shows ratio of Cinnamons
and Cinnamon Opalines as 1:1

You can see that you will produce Cinnamons (cocks and hens) and Cinnamon Opalines (cocks and hens) in the ratio of 1:1. If you then mate a Cinnamon Opaline cock to a Cinnamon Opaline hen, then you will produce 100% Cinnamon Opalines (both cocks and hens) from this pairing.

Therefore, to answer your question that Cinnamon Opaline cocks are very rare, they may be rare because breeders do not deliberately set out to breed them, but as the diagrams show, in just three generations, it would be possible to embark upon a breeding programme that would fill your flights to overflowing with them.

The method that I have described is the classic method of establishing a mutation as a new variety. If you think about it, all breeds of pedigree dog are kept substantially different from each other only by isolation of each of the breed's gene pools. I remember when Rottweilers were very uncommon, it is only now that their popularity has increased, that breeders produce more litters to satisfy the increased demand and hence they are no longer uncommon. If budgerigar breeders wanted to produce the Slate variety as the only variety of domesticated budgerigar, then it could be done as easily as producing Normal Greens.

Editors' note: I regret that Dr Pilkington is unable to answer any further questions.

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