Glossary 

Chromosome: A contiguous block of DNA that is passed from parent to child after recombination.

Gene: A section of DNA on a chromosome that codes for a protein. Genes are the basic unit of heredity passed from parent to child.

Allele:  An allele is a particular version of a gene sequence which controls differences in phenotype (eg what color an animal will be). A gene can have one or more different alleles that control one or more different traits.

 
Locus: A term used to describe where on a chromosome a gene or allele resides.

Genotype:  The  DNA sequence of alleles that an individual carries.

Phenotype: The visual appearance of an individual. It is the instantiation of the genotype the individual carries.

Haploid:  A cell with a single set of chromosomes.

 
Diploid: A cell with two sets of chromosomes (one from each parent). 

Co-dominant: refers to a type of inheritance in which two versions (alleles) of the same gene are expressed equally which results in a display of traits from both alleles.

Partial/Incomplete Dominance: Refers to when a dominant allele does not completely mask a recessive allele which results in a blend of the two.

 
Dominant:  Refers to an allele of a gene which fully masks the phenotype of another allele that is recessive to it.

Recessive: Refers to a gene that needs two alleles to express as opposed to one with dominance.

Homozygous: An individual with matching alleles from both parents at a locus.

Heterozygous: An individual with miss-matched alleles from each parent at a locus.

Inheritance: The alleles passed from parent to child.

Cultivar: A selected-for trait that didn't originally come from the wild in its current form.

Morph: A color/phenotypic trait that is shared amongst an entire subgroup of a species or population.

Variation: Individual differences (mutations) in genes that result in phenotypic differences. Variations are not fixed in the entire population or a subgroup. 

Variable trait/Expressivity: A trait that shows high amounts of variation while still remaining genetically the same.

Penetrance: The chance of a phenotype being expressed when an individual carries a particular genotype. Individuals who carry a mutation with incomplete penetrance may appear as wild type even with a dominant allele.

Strain:   A genetic variant of a line with the same mutation (e.g. P. scaber 'Moo Cow' and 'Dalmation' are strains of the same mutation).

Line: A group of animals homozygous for an allele that belong to a lineage, obtained by inbreeding. A line-bred population will have similar genetic traits achieved through the selection of desired phenotypic traits.

Wild Type: A term used to describe the state of a gene in its most common form in that species.

Breed true: Two parents with matching phenotypes produce offspring, all of which have the same phenotype.

Albinism: A trait in which individuals lack or have significantly reduced production of melanin. Resulting in a yellowish/white individual with typically red eyes.

Leucism: A trait in which individuals lack or have significantly reduced production of all pigment cells, unlike albinism which only affects melanin. Resulting in a pure white coloration. 

Piebaldism: Having only two dominant colors in patches. It's form of leucism in which some portions of the animal still produce pigment cells. Piebaldism is often called partial albinism but this isn't correct as albinism prevents all melanin production meaning partial albinism can not exist.

Xanthism: Lack of melanin and pheomelanin resulting in an all/mainly yellow individual. Usually seen in vertebrates.

Axanthism: Lack of melanin and xanthophores resulting in a pink, red, dark red, or blue individual. most commonly seen in frogs which appear blue.

Melanistic: An individual with an excess amount of melanin which usually results in an all-black or much darker individual. The most common example of this is the "black panther" which is just a highly melanistic jaguar or leopard.

Amelanistic: A lack of melanin resulting in an all-yellow individual. In herpetoculture it is described to retain all pigmentation in the eyes but lack melanin in the rest of the body, unlike albinism which reduces melanin throughout the entire body including the eyes but in reality, it is the same mutation as albinism.

 
Pheomenalistic: An individual with excess amounts of pheomelanin resulting in a reddish brown or red individual while still retaining some melanin.

Calico: In isopods is a sex-linked trait expressed by females which typically results in mottled coloration. 

Sex-linked: Refers to characteristics (or traits) that are influenced by genes carried on the sex chromosomes.

Sex-limited: Genes that are present in both sexes but are expressed in only one sex and have no penetrance or are simply 'turned off' in the other.

Sex-influenced: Traits that are influenced by sex hormones usually developing as sexual maturity is reached.