Glossary of Genetic Terms

Genetics can be daunting to many individuals. We have tried to make this glossary as simple as possible. Please contact us if we have missed a term you are interested in, or the definitions are not as simple as they can be.

Albino - An animal with a genetic mutation where no melanin is produced.

Alleles - The different forms of a gene. A and a are different alleles of the gene that determines albinism. Alleles occupy the same locus, or position, on chromosomes.

Amelanistic - An animal with a genetic mutation where no melanin is produced. Same as Albino.

Anerythristic - A mutation showing reduced or no red color. Anerythristic snakes are generally black & white.

Axanthic - A mutation showing reduced or no yellow color.

Codominant - A mis-used term in the reptile world. The more correct term is incomplete dominant. It is when the heterozygous animal has a different, intermediate phenotype compared to the homozygous dominant or homozygous recessive individuals. A classic example of this is the Lesser Platinum mutation, where the heterozygous individual (Pp) is a Lesser Platinum, but the homozygous phenotype (PP) is Leucistic.

Dominant - A trait expressed preferentially over another trait.

Heterozygous - Differing alleles for a trait in an individual, such as Aa.

Homozygous - Both alleles for a trait are the same in an individual. They can be homozygous dominant (AA), or homozygous recessive (aa).

Hypomelanistic - An animal with reduced melanin.

Leucistic - A pure white snake with dark eyes. The homozygous phenotype of Lesser Platinum, Mojave and Fire mutations.

Melanin - Black skin pigments.

Melanistic - An animal with excessive melanin expressed - usually a black individual.

Mutation - A change in the DNA sequence of a gene to some new, heritable form.

Phenotype - The physical appearance of an organism with respect to a trait, i.e. normal (A) or albino (a) trait. The dominant trait is normally represented with a capital letter, and the recessive trait with the same lower case letter.

Punnett Square - A diagram designed by Reginald Punnett and used by biologists to determine the probability of an offspring having a particular genotype. It is made by comparing all the possible combinations of alleles from the mother with those from the father.

Recessive - The opposite of dominant. A trait that is preferentially masked by a dominant allele causing the phenotype to be expressed only in the homozygous recessive state (aa).

Tyrosinase - An enzyme required to synthesize the black pigment melanin.

Tyrosinase-negative - An albino whose cells lack tyrosinase, an enzyme necessary for melanin production. Tyrosinase-negative animals are albinos. This is the most common albino mutation.

Tyrosinase-positive - An albino animal which is capable of synthesizing tyrosinase, but not melanin. This indicates that there is another mutation in the melanin pathway, causing no melanin to be formed. This is a commonly mis-used term for any albino that is different in color. The only way to tell if an animal is tyrosinase-positive is to have a sample tested for enzymatic activity.

Wild-type - The non-mutant form of a gene, encoding the normal genetic function.

Xanthic - An animal possessing enhanced yellow color.