Dr John Pilkington answers questions on Genetics

Question to Dr John Pilkington from John Cave

Question: My best hens are Cinnamon-Opaline Green, their father is the best cock bird that I have. He is a Normal Cinnamon Green. Their mother also was a Cinnamon-Opaline Green. I want to get rid of the Cinnamon factor, but since it is recessive and seems to appear regardless of how I mate the hens. I've kept all the hens from this pairing since they are the biggest and buff type with good head size. I would like to eliminate the Cinnamon factor but don't know how using these hens. Any suggestions would greatly be appreciated.

Answer: The genes for Cinnamon and Opaline are both located on the X chromosomes of the sex chromosomes, and as such, they are termed sex-linked. There are two different types of sex chromosome, X and Y :in avians, the male has the XX genotype and the female has the XY geneotype, and since your hens are Cinnamon Opalines, it is obvious that both Cinnamon and Opaline genes are on the same X chromosome (because a hen has only one X chromosome). When both Cinnamon and Opaline genes are on the same chromosome, as in your hens, the two genes are said to be linked. (I suggest that you read my answers to Questions 2 and 14 , which cover this topic also).

When genes become linked, the two genes are inherited both together, therefore, if the Opaline gene is inherited by an offspring, then the Cinnamon gene will also be inherited. In the case of a male bird, the situation is a little more complicated. Since the cock possesses two X chromosomes, then there are more genotypes involving the Cinnamon and Opaline genes. If the cock has one X chromosome which has both Cinnamon and Opaline genes on the same chromosome, i.e., Xco, and the other has neither Cinnamon or Opaline genes, i.e., X, then the Xco X genotype is said to be Type I. But if the Cinnamon and Opaline genes are on different chromosomes with a geneotype Xc Xo, then this genotype is said to be Type II. In both Xco X and Xc Xo genotypes, although both cocks would possess just one Cinnamon gene and one Opaline gene each, the breeding behaviour of both birds would be very different, and both birds would appear as Normals.

For a cock to appear as a Cinnamon-Opaline he would have to have two Type I chromosomes, i.e, Xco Xco. A cock may appear as a Cinnamon with one Type I X chromosome, i.e., Xco Xc, or he may appear as an Opaline with one Type I X chromosome, i.e., Xco Xo.

Because of the more complex genotypes available in the male, with regard to the sex-linked genes, then if you wish to eliminate one of the sex-linked genes from your stud, it is more reliable and easier if you discard all your Cinnamon-Opaline Cocks (and any other Cinnamon Splits) and keep just your very best Cinnamon-Opaline hens. If you wish to eliminate the Cinnamon gene from the hens, because the Cinnamon and Opaline genes are linked on the same X chromosome, you will also eliminate the Opaline gene also, and the way to do it is as follows:

Pair your Cinnamon Opaline hens to your best Normal cocks (definitely not split for Cinnamon) in whatever colour you like (but please don't use Greys, otherwise you'll have a similar problem in future of being over-run with Greys!!!!) as follows: XX x Xco Y produces 50% Xco X Normal/ Cinnamon-opaline cocks 50% XY Normal hens
Discard all the cocks and keep all the hens which will all be Normals.

Hey Presto - You have done your clean up in just one generation!!!!

Since your best cock is a Cinnamon and all your best hens are Cinnamon-Opalines, if I were you, I would not be too worried about the Cinnamon gene at this stage: I would develop a family from this nucleus of budgerigars, and keep the family separate from your Normals. In this way, you will improve the quality of birds in your stud and at a later stage you can always improve your Normals by using your Cinnamon-Opaline hens, in the way that I have suggested.

If you are producing a lot of high quality Cinnamon-Opaline hens, then you have the best foundation of all for the development of a successful stud - it is far easier to buy good quality Normal cocks because nobody sells high quality hens!

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

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