Basic Genetics of Heritable Eye Disorders

Most heritable ocular disorders are transmitted as autosomal recessive genes. The GENOTYPE of an animal represents its genetic makeup relative to a given trait i.e.: normal, carrier or affected, while the PHENOTYPE represents the physical makeup relative to that trait i.e. normal or affected. An animal with a normal PHENOTYPE, may be genetically normal, or may be a carrier. In certain diseases where the onset of the disease is not noted until later in life, the animal may have a normal phenotype before onset of the disease, but is genetically affected.

For diseases with autosomal recessive mode of inheritance:

RR represents a genetically normal animal
Rr represents a carrier animal
rr represents an affected animal.

How to read these tables:

Table 1: Normal X Carrier

Table 2: Normal X Affected

Table 3: Carrier X Carrier

Table 4: Carrier X Affected

Table 5: Affected X Affected

For diseases with autosomal dominant mode of inheritance:

In dominantly transmitted genetics, heterozygous affected animals may be affected to a lesser degree than homozygous animals. There are a few factors which may confuse the distribution numbers of the condition in the progeny. Some heterozygotes may appear phenotypically normal under a phenomenon known as "incomplete penetrance". In some conditions, homozygotes die in utero, while heterozygotes survive.
dd represents a genetically normal animal
Dd represents a heterozygous affected animal
DD represents a homozygous affected animal.

Table 6: Normal X Heterozygous Affected

Table 7: Normal X Homozygous Affected

Table 8: Heterozygous Affected X Heterozygous Affected

Table 9: Heterozygous Affected X Homozygous Affected

Table 10: Homozygous Affected X Homozygous Affected