|MadSci Network: Zoology|
Albinism in psittacines (parrots) appears to be reasonably well studied due to the presence albinism in budgerigars. I found the following web site with lots of information about this: http://www.euronet.nl/users/hnl/pigment.htm Generally, albinism is a recessive genetic trait causing a defect in the biochemical pathway that produces melanin. The most common form of albinism results from a defect in the enzyme tyrosinase, which is used to process the amino acid tyrosine into melanin. The common form of melanism in birds can be either sex-linked (the gene is on one of the sex chromosomes, which in birds are designated as Z and W) or autosomal (the gene is on one of the other chromosomes). Because female birds are hemizygous (ZW) if your birds were carrying a sex-linked gene for albinism one would expect the female to be albino more frequently than the male. As you had two albino males and a normal female your parent birds are probably carrying an autosomal allele for albinism. Is having two out of three offspring albino unexpected? Under normal Mendelian inheritance an autosomal recessive trait is expected to be phenotypically expressed in one quarter of the offspring. At first glance it would appear that 0.67 is much greater than 0.25. If one were trying to make a judgement from this single clutch our statistical power to tell if 0.25 is significantly different from 0.67 would be reduced by the small sample size (3). However, as you mention that these parents have had about 20 normal chicks then it would appear that having two albinos out of twenty is not too unexpected (0.25 expected, .10 seen). Are these males twins? I haven't found any data on twinning in birds, though I expect that it would be a difficult phenomenon to judge. One molecular genetic technique that could be used to test this is microsatellite analysis. This technique has been used to assess paternity and maternity (egg dumping) in wild birds. If you could find a genetic lab at a university around you this sounds like it would be an interesting one semester project for a beginning graduate student.
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