Basic definitions:

Homozygous – A state in which both genes for a specific trait are the same. When a recessive gene is it its homozygous form, it makes the animal look different from the wild-type. i.e. (recessive morphs: Marble, T- Albino, T+ Albino & Granite expressions for example)

Heterozygous – possessing two different genes for a given trait. An animal with one mutated, recessive gene still appears normal; its mutated gene can be inherited by future offspring. Het – an abbreviation for heterozygous. 

Double Heterozygous – being heterozygous for two different homozygous traits. DH – an abbreviation for double heterozygous.

Possible Het. – an animal from a known breeding that has either a 50% or 66% possibility of being “heterozygous” for a mutant gene. A 66% possible het comes from breeding 2 heterozygous animals together and must be bred out to determine which animals are really Hets as visually you cannot tell the difference. 

Normal – an animal with no mutated genes – “wild type” in appearance.

Genotype – an organism’s genetic composition. Heredity – the transmission of genetic characters from parents to offspring. 

Phenotype – an animal’s external appearance, as caused by its genotype. 

Recessive – a gene that affects an animal’s appearance if it’s present in the homozygous state. A heterozygous animal carrying a mutated recessive gene looks normal. 

Albino – having absent or deficient melanin. See tyrosinase-negative and tyrosinase-positive. 

Tyrosinase – an enzyme required for synthesizing melanin. 

Tyrosinase-negative (T-) – an albino whose cells lack tyrosinase, producing a white and yellow/orange animal with pink eyes and pink tongue. A separate albino mutation from tyrosinase-positive.

Tyrosinase-positive (T+) – an albino not able to synthesize melanin, but capable of synthesizing tyrosinase, which results in lavender-brown skin colour. Also referred to as a caramel albino.

Melanin – black or brown skin pigments. 

Amelanistic – lacking no melanin. 

Anerythristic – lacking red colour. 

Axanthic – having no yellow colour. 

Hypomelanistic – an animal having less black and/or brown colour than a wild-type.

Hypermelanistic – abnormally dark, especially due to an increase of melanin. 

Leucistic – a pure white animal with dark eyes.