Care Sheets


Glossary of Genetic Terms


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 (black pigment) 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.

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