Question to Dr John Pilkington from Dolores Noonan

This is quite a tricky question to answer Dolores, not because it's difficult to answer, but because the operation of the Dilute gene is somewhat different to most of the other colour genes in budgerigars, because it is one type of a multiple allelomorph group which includes Greywings, Clearwings and Dilutes.

As we all know, the "wild type" budgerigar is the Normal Light Green, and since the budgerigar has been bred in captivity, a number of genes, which give the wild type budgerigar its usual appearance, have mutated which give rise to the varieties that the budgerigar breeder selects for "improvement". To date more than 25 different colour mutations have been identified, and bred specifically as varieties; most of these mutations are either dominant or recessive to the Normal wild type gene for each character that they modify.

If we look at, say, the Blue variety, the mutated gene is recessive to the normal Green gene. The Green/Blue gene system is located on one pair of chromosomes, and if we represent the dominant Green gene as G and the recessive Blue gene as g then there are the following different gene pairings.

This example shows that although the recessive Blue gene may be present throughout a stud to the same extent as the dominant Green gene, the display (phenotypes) of the Blue gene in the individuals within the stud will be approximately 25% of individuals if the birds are to mate at random. From the above possible pairings, it can be seen that the only pairing that will produce Blue phenotypes (gg genotype) in any number is the Blue (gg) × Blue (gg) pairing, and this would mean a deliberate breeding plan to breed Blues. This example shows the workings of all recessive genes.

In the case of the multiple allelomorph gene system Greywing/Clearwing/Dilute, the wild type gene which controls the strength of colour has mutated not just once but three different ways, all at the same locus (position on the chromosome), and each of the three different mutations has reduced the strength of pigmentation by differing amounts; the Greywing the least and the Dilute the most. Since the three different mutations have occurred at the same locus and involves just one gene system, then a budgerigar can only possess one of the four different alleles on the relevant chromosome, either a Normal body colour strength gene or a Greywing gene or a Clearwing gene or a Dilute gene at the same locus on the chromosome.

The Normal body colour strength gene is dominant to all of the other recessive mutations of this gene, however, the Greywing gene is Dominant to the Clearwing and Dilute genes, and the Clearwing gene is dominant to the Dilute gene; this gene system has a hierarchy of Dominance as in the diagram:

• Ccg
• cwcw
• cwcd
• cdcd

where the dominant

• Normal=C
• Greywing=cg
• Clearwing=cw
• Dilute=cd

Since the C gene is dominant to the cg, the cw and the cd genes then a budgerigar of Normal colour strength may have any of the following chromosome pairings:

• CC
• Ccg
• Ccw
• Ccd

The Greywing may have any of the following chromosome pairings:

• cgcg
• cgcw
• cgcd

The Clearwing may have either of the following chromosome pairings:

• cwcw
• cwcd

However, the Dilute may only have the following chromosome pairings:

• cdcd

Original text Copyright © 1998, Dr John Pilkington

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

Other pages in this section

Budgerigars Galore Homepage | Contents Index | Beginners | Breeding | Breeding Charts | Diseases | General Interest | Genetics | Links | Management and Nutrition | New Zealand News | Noonan Aviary | Popular Varieties | Rare Varieties | Show Preparation | Specialist Varieties | Tips |

Web page copyright © 1999, Dolores Noonan. All rights reserved.

Designed and created by Arcadia WebSite Design.