Dr John Pilkington answers questions on Genetics

Question to Dr John Pilkington from Amanda Sacco

Question: I own an Albino Budgie, how does this happen, and have they got any disabilities?

Answer: The name Albino is derived from the Latin word Alba which means white, but in the case of any individual within a species which is described as an Albino, not only is the individual white in colour, but it is also devoid of the pigment melanin in all parts of the body, and as a consequence the Albino always has red eyes.

In budgerigars, there is a single gene which operates in a manner similar to a "master switch" which controls the overall production of melanin. This gene has mutated so that the production of melanin is prevented, and it is named the Ino gene and is located on the X chromosome. It is therefore, said to be sex-linked, since the chromosomes which determine the sex of the individual, also control the overall production of melanin within the body.

Like all the other known sex-linked genes in budgerigars, the Ino gene behaves as a recessive gene, thus for the individual to appear as a visual Albino, then if the bird has two X chromosomes then both X chromosomes must possess the Ino gene - since only the cock has the XX genotype, then only the XiXi genotype will appear as Albino, and XiX or XX will appear as Normal (non-Albino).

In the case of the hen, since her sex chromosome pair are made of one X chromosome and one Y chromosome, she has the XY genotype and for a hen to appear as a visual Albino, she must have the XiY genotype. The only pairing which produces 100% Albino offspring is the pairing together of two Albinos: XiXi x XiY = 50% XiXi Albino cocks 50% XiY Albino hens

The pairing of an Albino cock to a Normal hen will produce 50% Albino hens and 50% Normal /Albino splits cocks: XiXi x XY = 50% XiX Normal / Albino split cocks 50% XiY Albino hens

The pairing of a Normal /Albino split cock to an Albino hen will produce lesser numbers of Albinos in both cocks and hens: XiX x XiY = 25% XiXi Albino cocks 25% XiX Normal / Albino split cocks 25% XiY Albino hens 25% XY Normal hens

The pairing of a Normal /Albino split cock to a Normal hen will produce only 25% Albino hens: XiX x XY = 25% XiX Normal / Albino split cocks 25% XX Normal cocks 25% XiY Albino hens 25% XY Normal hens.

Although the Lutino is yellow and not white in colour, it is in fact an Ino - a budgerigar without melanin pigment, and this fact is evident because the eyes of the Lutino are red. The reason that there is a visual difference between the Albino and the Lutino is due to the fact that there are two separate pigment systems in the budgerigar:

The melanin pigment system .
"psittacin" (yellow) pigment system.

Budgerigars which possess yellow pigment are classified as Green series birds, and budgerigars which have no yellow pigment (except Yellowfaces) are classified as Blue series birds.

Therefore, the Albino has neither melanin nor yellow pigment, whereas the Lutino has no melanin pigment but does have yellow pigmentation.

The mating of an Albino with a Lutino will produce 100% Inos, but since the Albino is a Blue series bird and the Lutino is a Green series bird, the ratio of Albinos to Lutinos produced will be exactly the same as if the birds were Blue and Green only, because the Green/ Blue gene system is acting independently from the Ino gene system.

The evolutionary purpose of melanin is that it protects the contents of cells (the DNA molecules in the chromosomes in particular) from the harmful effects of Ultraviolet radiation, and since the Albino has no melanin, then the unprotected cells tend to suffer damage from uncontrolled exposure to the harmful effects of the sun, hence Albinos do not survive in the wild. Also, if an Albino appeared in the wild, then its chances of survival would probably be less than that of non-Albinos due to predation.

Further, Albinos prefer lower light levels because there is no pigmentation in the eyes, thus the amount of light entering the eye cannot be controlled by the iris, as in the normal eye. However, in the protected environment of a bird room, the level of UV light is considerably less than in the open of the Australian bush, and so Albinos in captivity, unless forced to remain in the unprotected outdoors, show no ill-effects from their genetic condition.

The two types of Ino, show no health problems as a consequence of the absence of melanin - it certainly does not increase mortality, nor adversely affect longevity. The fertility of the Inos is of the same level as other budgerigars, and so one can say that no deleterious effects are suffered as a consequence of the absence of melanin pigmentation. However, if specialist Ino breeders know of detrimental health effects suffered by Inos, then I would be grateful for any information on this subject.

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

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