How are the mutations inherited?
Genes come in pairs; a pair is composed of a gene from each parent. A mutation can affect both copies of the gene, only one copy, or neither. The different combinations of gene pairs alter the way in which the mutation affects the bird; the effects of these combinations are determined by whether the mutation is dominant, recessive, or sex-linked. A dominant mutation needs only to be present in one copy of a gene to change a bird’s appearance. Normal grey (which is not considered to be a mutation, but the wild coloration of a cockatiel) is dominant to all recessive and sex-linked colors. The two true dominant mutations are dominant silver and dominant yellowcheek. A bird with one dominant silver gene will appear silver, and is called a single-factor bird. A cockatiel with two copies of the gene is called a double-factor. The two forms can be told apart visually; a double-factor is much paler than a single-factor (think of the double-factor as having inherited a double dose of melanin re
