AVIAN GENETICS

The next category of chromosomes to be discussed is the autosomes. Autosomes are all the chromosomes that are not sex chromosomes. In the fertilized egg, autosomes occur in pairs. These pairs are referred to as homologues.

Some of the more common autosomal genes for avian coloration and pattern include:

For a more complete listing and explanation of parrot color mutations, refer to "A Guide to Color Mutations and Genetics in Parrots" by Terry Martin.

Since autosomes occur in pairs containing equal numbers of genes, regardless of sex, there will always be at least two alleles present for a trait. The hemizygous condition does not apply to autosomes (exception being a deletion mutation that survives). You will notice that most of the mutations are recessive. Therefore, in order for the recessive mutation to be expressed, it must occur on both homologous chromosomes - the homozygous recessive condition. If the mutation is recessive and only occurs on one homologous chromosome, while the wild-type gene resides on the other homologue, then this is a heterozygous condition and the wild-type phenotype will be displayed.

Figure 10 shows a cross between a Recessive Pied Male (r,r) and a Normal heterozygous for Recessive Pied Female (+,r). The offspring from this cross will be 50% Pied (r,r) and 50% Normal heterozygous for Pied (+,r). Obviously, half of each will be males and females.