III. AUTOSOMAL GENES
Genes are made up of DNA and control the transmission of hereditary characteristics. The expression of the hereditary characteristics -- which for our purposes will be the plumage color -- is called the phenotype. The genotype is the genetic makeup of the individual bird. As we will see later, the genotype may vary while still producing the same phenotype.
Chromosomes are located within the nucleus of a cell and carry the genes. There are two categories of chromosomes -- autosomes and sex chromosomes. Autosomes are any chromosome other than a sex chromosome. There are four autosomal recessive genes for color in the ringneck dove. These four include: albino (gene symbol = al), ivory (gene symbol = iv), pied (gene symbol = pi), and rosy (gene symbol = ry). Tangerine (gene symbol = Ta) is an autosomal co-dominant. Frosty (gene symbol = Fr) is likely a co-dominant also, but that is not yet conclusively proven.
Autosomal recessives: Since autosomes occur in pairs (unlike the sex chromosomes), both males and females have equal numbers of genes on the autosomes. Most of the autosomal genes are recessive and require that both mutant genes be present if the mutant color is to be expressed. For these recessive mutants, the non-mutant allele is the dark (wild type) allele. The dark (wild type) phenotype really is not only sex-linked but results from the normal color allele at any locus with a mutant color. The allele to albino is dark. The allele to ivory is dark. The allele to pied is dark. The allele to rosy is dark. When this wild type allele is present on one chromosome of a pair the dark (wild type) phenotype will be displayed. This is a heterozygous condition.
For example: a cross between a dark (wild type) male and a pied female will produce all dark offspring. All these dark offspring will be heterozygous carriers of pied. The same will be true if the cross is between a dark and any of the other single mutants -- albino, ivory, or rosy. If we cross these heterozygous darks the result will be offspring produced in a theoretical 1:2:1 ratio. The following Punnet Square shows this graphically. We will use "+" to represent the dark allele (wild type) and "pi" to represent the pied allele. The slash mark in the diagram stands for the chromosome on which the "+" or "pi" allele is located. We will place the male gametes across the top horizontal of the square and the female gamete down the left vertical of the square.
| + | pi | |
| + | +//+ |
pi//+ |
| pi | pi//+ | pi//pi |
Offspring Genetypes and Phenotypes
|
1/4 +//+ |
Homozygous Dark |
| 2/4 pi//+ | Heterozygous Dark |
| 1/4 pi//pi | Pied |
Three of four offspring will show as dark. Two of the three will be heterozygous dark//pied. The homozygous recessive will show as a pied. This ratio is the expectation of the average and may take more than four offspring to prove true.
Autosomal Dominants: Frosty and tangerine are codominants and should show in almost any
color except albino. The color, tangerine, is produced by a heterozygous genotype (Ta//+) while the color, tangerine pearled, is produced by a homozygous genotype (Ta//Ta). The pearling effect and the white neck ring of the tangerine pearled is due to the pleiotropic action of the tangerine gene in the homozygous condition. (Pleiotropy is the action of a single gene resulting in multiple phenotypic expressions.) The mottled iris seen in ivory doves is also a pleiotropic effect of the ivory gene in the homozygous condition.
The color frosty (Fr//+) is seen in the heterozygous genotype. No one has established conclusively what the homozygous frosty (Fr//Fr) looks like. The frosty gene has the general action of lightening the wild type color.
For a more detailed and scientific discussion of the autosomal recessive genes, refer to Dr. Wilmer J. Miller's website (www.ringneckdove.com).
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