I. Definitions
It is helpful to understand a few basics of genetics before proceeding to look at the various mutations in the ringneck dove (Streptopelia risoria) and the expected outcome from various mutation crosses. We will start with some simple definitions, which will hopefully create some familiarity with terms. When we are comfortable with the terms then the subject of genetics doesn't seem quite so difficult.
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.
The color standard of reference is the wild type or normal which is a Dark. The plumage is a dark gray with a distinct violet head and breast. The 40+ color mutations come from this wild type or dark color. In the process of mutation, a gene is changed into two or more alternative forms called alleles. Alleles are one of a group of genes that occur at a given locus on the chromosome. The term gene and allele are sometimes used interchangeably depending on emphasis of meaning.
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. Sex is determined by a heteromorphic (meaning dissimilar) pair of chromosomes called sex chromosomes. In mammals these chromosomes are labeled X and Y. A male mammal has the XY and a female the XX complement. In birds, not only is the complement of the sex chromosomes the opposite of mammals, but geneticists also assign a different lettering to make the distinction. The letters used are Z and W.
A male dove is ZZ while the female is ZW. The important thing to remember is that the W chromosome carries no known active genes. This is important to know when we get to the sex-linked genes.A genetic difference is produced by a pair of genes -- one received from the male parent and one received by the female parent. (This is true except for the sex-linked genes where the difference in female birds is the result only of the gene on the Z chromosome.) If both genes are identical, the genetic makeup is called homozygous. If the pair of genes is different, then it is called heterozygous.
A dominant gene is one that can express itself to the same degree either in the homozygous or heterozygous state hiding an alternative form. A gene that can express itself only in the homozygous state is referred to as a recessive gene. There is also a condition called codominance, which exists for some genes. This means that gene has the ability to express itself to some degree in the heterozygous state. Tangerine is a proven codominant gene. Frosty is very likely a codominant gene, but that is not yet proven.
All the 40+ color varieties are mutant forms of various interactions and dilutions. Dr. Wilmer J. Miller's website (www.ringneckdove.com) gives a very helpful diagram of the single gene mutants and a summary of their combinational interactions.
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