Common Reptile Genetics Terminology & Definitions

Common Reptile Genetics Terminology & Definitions

Reptile Genetics 101 Common Terminology

Common Reptile Genetics Terminology

A good starting point in beginning to learn about reptile genetics is to familiarize ourselves with some of the most common terminology. You will find the compiled list of common reptile genetics terminology listed below to be great for quick reference. However, nearly every one of these terms are practically a whole field of research in and of themselves. So, there is much more to that can be learned about each of these genetical terms, depending on how far one would like to expand their knowledge of genetics.

Aberrant - Deviating from the ordinary, normal or expected.
Albundismus - A Type of Melanism in which the specimen is not completely black, but shows a change in the elements of the basic pattern as consequence of the number of isolated black spots or dots in the nonblack areas of the pattern.
Adaptation, biological - Alteration of structure or function to suit a particular environment.
Albinism - The heritable condition observed as the inability to form melanin in the skin and scales. Absence of pigment in animals usually pigmented; the state of having colorless chromatophores. Lacking pigment and therefore appearing pink or white. A genetic absence of tyrosinase. The appearance created by a lack of black pigment in the dermal and epidermal chromatophores.
Albino – Normal pigment is absent from the scales. The blood pigment hemoglobin is present and may result in pinkish specimens or specimens with red eyes. Having the absent or deficient melanin. Widely used term for "Amelanistic".
Allele - A shortening of the term allelomorph; one of two or more forms of a gene arising by mutation and occupying the same relative position (locus) on the homologous chromosome; may be distinguished by their differing effects on the phenotype. Either of the two paired genes which affect an inheritable trait.
Allophore - A cell or chromatophore containing red pigment in the skin of reptiles, amphibians, and fish.
Amelanism - A term sometimes used instead of Amelanistic. The appearance resulting from a lack of melanin.
Amelanistic - Having no melanin. The pigment melanin, which is responsible for black, brown, and yellow colors, is absent; specimens are pale in color, although they may have some color, especially red or pink, owing to the presence of other pigments. A single recessive mutation resulting in a lack of black pigment referred in both skin and eyes; bright red and orange predominate. Containing no melanin. The appearance created by the lack of all Eumelanin and BCM.
Amino acid - Any of the subunit building blocks that are covalently linked to form proteins. Organic compounds that are the building blocks of protein.
Anal scale - A single unpaired scale that covers the cloacal opening. Although it may be regarded as the posteriormost scale in the series of ventrals, the anal scale is not included in counts of the ventral scales.
Anerythristic - Having a lack of red pigment and all red markings. A mutation that can be caused by two separate defective genes resulting in a lack of red and orange pigment; predominantly marked with grays but also black, brown, or yellow. An appearance that is without red; and appearance usually assumed to be the result of reduced or absent Erythrophore pigment production in the skin.
Angle of the jaw - The area on the lateral surface of the head positioned above the articulation of the upper and lower jaw bones, usually at the widest area across the head.
Anomaly - A deviation from the ordinary, normal, or expected.
Anterior - An anatomical direction meaning toward the front or toward the head.
Anterior prefrontals - A single pair of large plate-like prefrontals in contact with the internasals and in full contact along the midline.
Appearance - The perceived outward aspect of a snake resulting from the combination of its color and pattern. Sometimes used as a synonym of phenotype.
Arboreal - Living in trees.
Axanthic - Frequently having a lack of yellow pigment; a term sometimes used instead of anerythristic, but not appropriately. In the descriptive sense, an appearance lacking the expected visual contributions from yellow or orange pigments.
Axanthism - Literally “without yellow". The absence of yellow or orange color. Absence of yellow pigment, or absent or deficient xanthophore pigment metabolism.
Azygous - Occurring singly; unpaired.
Backcrossing - Mating of an organism with a parent.
BCM - The acronym for black cellular material, an inclusive term to refer to all the chemical compounds of black pigment found in melanophores.
Bilateral - Occurring on both sides of an organism.
Biochrome - A pigment produced in a chromatophore.
Breed true - A phenotype for a trait is said to breed true if two parents with that phenotype produce offspring of that same phenotype exclusively. In reference to a familial trait that has been reproduced through inbreeding/line breeding enough generations so that the offspring when bred together will produce offspring exhibiting the trait in question.
Carotene - A yellow skin pigment widely distributed in animals (Holmes, 1979). Yellow pigment.
Carotenoids - Fat-soluble pigments widely distributed in animals and including carotene and xanthophylls.
Carotin - Same as carotene.
Character - An observable phenotypic attribute of an organism.
Chlorophane - A green chromophane.
Chromacyte - Any cell containing a pigment.
Chromatophores - Pigment cells. Cells in the skin that usually contain pigments of different colors. A colorless body in cytoplasm and developing onto a leucoplast, chloroplast, or chromoplast. Any cell that bears pigment and thereby plays a role in the overall color pattern of the animal.
Chromoblast - An undifferentiated pigment cell in an embryo.
Chromophane - Retinal pigment in lower vertebrates.
Chromosome - Occurring in the nucleus of a cell. Composed mainly of DNA and basic protein, and bearing the genes being arranged in linear order. Chromosomes are arranged in pairs with the genes being arranged on the chromosome. The presence of homologous chromosomes is referred to as the diploid state. Nuclear inclusion containing genes arranged in linear sequence. Each cell in every living thing has a nucleus. Much of the nucleus is made up of a constant number of paired chromosomes. Each chromosome is a single, long strand of DNA in a protein matrix. The strand of DNA contains many genes.
Circumoculars - The series of scales that rim the eye, including the preoculars, a single supracular, the postoculars, suboculars, and supralabials.
Cloaca - The common chamber in the body of reptiles and amphibians into which the reproductive, intestinal, and urinary ducts open. The external opening of the cloaca is termed the vent, anus, or cloacal opening.
Cloacae - Plural of cloaca.
Cloacal opening - The external opening of the cloaca; also termed the vent, or anus.
Co-dominant - A gene that causes the homozygous form to look different than the wild-type and the heterozygous form to have traits of both.
Complete dominance - See dominant gene.
Crossing over - The exchange of chromosomal material (parts of chromosomal arms) between homologous chromosomes by breakage and reunion. The exchange of material between nonsister chromatids during meiosis is the basis of genetic recombination. During meiosis, the breaking of one material and one paternal chromosome, resulting in the exchange of corresponding sections of DNA and the rejoining of the chromosome. This process can result in the exchange of alleles between chromosomes. Compare recombination.
Cysteine - A nonessential amino acid (meaning that the body can synthesis it) important in the synthesis of pheomelanin.
DNA (Deoxyribonucleic Acid) - Molecules bearing genetic information of all living cells. Gene. Also referred to as “unit of inheritance.” A molecule containing the genetic information of all living cells. A macromolecule usually consisting of antiparallel polynucleotide chains held together by hydrogen bonds, in which the sugar residues are deoxyribose. The primary carrier of genetic information. The molecule of heredity that encodes genetic information.
Designer appearance - Popular term referring to the phenotype resulting from the selective breeding to combine two or more appearances, each caused by a different mutation. See hybrid.
Dihybrid cross - Mating of individuals heterozygous for two separate inherited traits.
Dimorphism - Occurrence of two forms, distinct in color or other characteristic, among animals of the same species.
Diploid - Having two sets of chromosomes; the typical zygote arrangement of chromosomes. An individual with two chromosome sets in each cell, excluding the sexchromosome. See haploid.
Dominance series - Dominance relations of all possible pairs of alleles are arranged in order from most dominant to most recessive.
Dominant - A gene that causes an animal to look different than the wild-type and where the homozygous form and the heterozygous form look the same as each other. The normal form of the gene that is usually denoted by an uppercase symbol. An allele that determines the phenotype of the heterozygote. An allele that can determine the phenotype whether heterozygous or homozygous.
Dominant negative - Mechanism of dominance in which some alleles of genes encode subunits of multimers that block the activity of the sub units produced by wild type alleles.
Dominant suppression - A form of epistasis in which a dominant allele at one locus suppresses the effect of a dominant allele at another locus.
Dopa - 3, 4-dihydroxy-L-phenylalanine, an intermediate chemical in the synthesis of melanin.
Dorsal - Pertaining to the back; an anatomical direction meaning toward the back. The top, back, or uppermost surface of an organism.
Dorsolateral - Pertaining to the area between the dorsal and lateral surfaces.
Dorsum - The upper surface or back of a python.
Double Heterozygous - Being heterozygous for two different traits.
Ectopic expression - Gene expression that occurs out side the cell or tissue where the gene is normally expressed.
Ectothermic (Poikilothermic or cold-blooded) - Possessing no internal means for controlling body temperature.
Embryo - Organism in early stages of development, before it is physiologically independent.
Endothermic (Homeothermic or warm-blooded) - Having ability to maintain constant body temperature in different ambient temperatures.
Epistasis - The situation occurring when one allele of one gene obliterates the phenotypic expression of all other allelic alternatives of another gene. A gene interaction in which the affects of an allele at one gene hide the effect of alleles at another gene. Nonreciprocal interaction between genes such that one gene interferes with or prevents the expression of another gene.
Erythrism - Having red skin and scales caused by a lack of black pigments (eumelanin), which allows the red pigment (pheomelanin) to dominate the color of the appearance. Abnormal or excessive amount of red coloring. The occurrence of unusual amounts of redness in an individual or population as compared to the normal pattern of the species.
Erythrochromism - See erythrism.
Erythrocystic - See erythrism.
Erythrophores - Reddish-purple pigment-bearing cells. Cells containing carotenes or yellow pigment. Xanthophores that appear red.
Erythrophore - Red chromatophore.
Eumelanin - A form of melanin that is black or dark brown. Black or brown melanin. See phaeomelanin.
P generation - Two unlike individuals that begin a genetics experiment, or breeding program.
F1 generation - First filial generation; the offspring of the P generation. An F1 is a single member of the F1 generation.
F2 generation - Second filial generation; the offspring of two F1s.
F3 generation - Third filial generation; the offspring of two F2s.
Gene - A unit of heredity that determines the characteristics of the offspring.
Genetics - The study of heredity.
Genotype – An organism’s genetic composition. Heredity - the transmission of genetic characters from parents to offspring.
Het – An abbreviation for heterozygous.
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. A codominant animal is heterozygous for the dominant form of its mutated gene, yet is different in appearance than both the wild-type and homozygous forms.
Homozygous – A state in which both genes for a specific trait are the same. When a recessive gene is in its homozygous form, it makes the animal look different from the wild-type. When a dominant gene is in its homozygous state, it causes the animal to look different from both the wild-type and the heterozygous (codominant) forms.
Hypomelanistic - An animal having less black and/or brown color than a wild-type.
Leucistic - A pure white animal with dark eyes.
Locus - A gene's position on a chromosome (plural: loci)
Melanin - Black or brown skin pigments.
Melanistic - Abnormally dark, especially due to an increase of melanin.
Mutation - An abnormal gene that under certain circumstances can cause an animal to be born with an appearance other than wild-type.
Normal - An animal with no mutated genes - "wild type" in appearance. (See wild type)
Phenotype – An animal’s external apperance, as caused by its genotype.
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: 50% of the offspring are heterozygous, 25% will be homozygous, and 25% will be wild-type. Of the normal appearing animals, 66% (or roughly 2 out of 3) will actually be heterozygous for the mutated gene.
  • A 50% possible het comes from breeding a heterozygous animal to a wild-type animal. All of the resulting offspring will be wild-type in appearance, but 50% of them will actually be heterozygous for the mutated gene and must be bred out to determine which animals are really hets.
Punnett Square - A learning tool for determining the possible outcomes of a given cross between individuals. It was developed by R.C. Punnett, an early British geneticist.
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.
Super - Commonly used herpetocultural term for the dominant form of a co-dominant mutation. i.e. Super Pastel
Triple Heterozygous - Heterozygous at three gene loci.
Tyrosinase - An enzyme required for synthesizing melanin.
Tyrosinase-negative - An albino whose cells lack tyrosinase, producing a white and yellow/orange animal with pink eyes. A separate albino mutation from tyrosinase-positive. Also called T-.
Tyrosinase-positive - An albino not able to synthesize melanin, but capable of synthesizing tyrosinase, which results in lavender-brown skin color. Also referred to as T+.
Wild-type - The way the animal usually looks in nature (i.e. the normal color and pattern).
Xanthic - Having more yellow color than wild-type.


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Topic: Reptile Genetics 101
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Shamika White
Nov 2018
Shamika White (Evansville, Indiana, US) says...

This site was very helpful and explained things much better than some of the other sites.

Aug 2017
Novalar says...

Good article!

Wendy Otteni
Dec 2016
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Wendy Otteni (Albion, Pennsylvania, US) says...

Definitely everything you need to know about snakes right here......ths site is amazing!

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