Cat Modes of Inheritance
Autosomal Dominant Inheritance
For an autosomal dominant disorder, only one copy of a given allele is necessary to produce the trait. If an animal receives an abnormal allele from one parent and a normal allele from the other parent, the abnormal trait will be expressed.
Autosomal Recessive Inheritance
With an autosomal recessive genetic disorder, an animal must receive two copies of the abnormal gene (one from each parent) in order to show signs of the disorder. In most situations, this occurs when both parent animals are asymptomatic carriers of the disorder.
Because the disorder is recessive, an animal who carries one copy of the abnormal gene and one copy of the normal gene will not show signs of disease. If two parents who are carriers are bred, however, 25% of their offspring will receive two abnormal copies of the gene and thus express the genetic disorder. Another 50% of their offspring will receive one abnormal copy of the gene and thus be genetic carriers of the disorder. Finally, 25% of their offspring will receive two normal copies of the gene and be unaffected.
Sex-linked Inheritance
Male and female animals differ in their sex chromosomes. A male animal carries one X chromosome (received from his mother) and one Y chromosome (received from his father). A female animal carries two copies of the X chromosome (one from each parent). Because the Y chromosome is dominant, XY animals are male and XX animals are female.