Crested Gecko Genetics - The Basics

I am by no means a scientist. But - this article set should help with understanding basic genetics.

Simplified terms for those who want a basic understanding of reptile genetics. Much of the crested gecko genetics have not been proven due to the lack of a known normal/wild-type without mutations. However, Mendelian genetics do apply.

Trait – Physical attributes – pattern, color, structure.
Morph – Set of specific trait characteristics in a distinct, repeatable form.
DNA – Genetic code of all living things.
Gene – DNA of physical and non-visual inherited characteristics.
Normal/Wild-type – Phenotype most common in a general population.
Mutation – Any variant allele from the normal/wild-type gene.
Phenotype – Observable characteristics, physical traits.
Genotype – Set of alleles.
Alleles – A pair of genes located at a certain locus that determine inherited characteristics.
Locus – Location on the DNA strand.
Heterozygous – (het) – Paired alleles that are different, usually one dominant and one recessive. Hets can be gene carrier, but do not visibly show the recessive. Two hets for the same gene have the ability to produce a visual.
Possible heterozygous – (pos het) – Unproven possible recessive gene carrier. Expressed in percentages of probability of carrying one recessive allele.
Homozygous – Paired alleles that are the same.
Visual – Physically displaying a gene.
Super – Matched pair of a codominant gene.
Dominant – Produces a visual even when only one allele for the mutated gene is present. Same physical appearance whether heterozygous or homozygous.
Recessive – Cannot produce a visual form unless homozygous alleles are present. Axanthic and Super Stripe follow recessive expression.
Codominant – Alleles of the same gene are equally visual. Simple scale example: red allele and white allele produces separate red and white scales.
Incomplete dominant – One allele not completely expressed over the second allele. Alleles that blend; the heterozygous pair will have a different form than a homozygous pair. Simple scale example: red allele and white allele produces blended pink scales.

A majority of the messages we receive are regarding genetics – especially recessive carriers: visual vs het vs pos het percentage. This article is here to de-mystify these terms for you! After all, recessive projects can be one of the most rewarding endeavors in the reptile community.

For general genetic terms check out our Super Simple Genetics post.

Key – Visually expressed in letters I = dominant allele, i = recessive allele.
II = no recessive component, no chance of producing hets or visuals
Ii = het for recessive gene, carries but does not display
ii = visually displaying recessive gene

Visual – Animal has two recessive alleles and displays the gene visually. Will always pass one recessive allele to offspring. Expressed as ii.
100% het – Non-visual for recessive gene, but carries. Has one dominant allele and one recessive allele. Can pass either one dominant allele or one recessive allele to offspring. Expressed as Ii.
66% het (or 66% pos het) – There is a 2 in 3 (66%) chance the animal is a 100% het recessive gene carrier. This means the animal is not guaranteed to carry recessive gene as hets do not visually display. Expressed as 33% chance II or 66% chance Ii.
50% het (or 50% pos het) – There is 1 in 2 chance (50%) that the animal is a 100% het recessive gene carrier. Expressed as 50% chance II or 50% chance Ii.

MorphMarket has a handy ball python genetic calculator that can be used for some crested gecko genetic calculations. Axanthic is recessive, so to be a visual the animal must carry two recessive alleles for axanthic.

Example of a visual x visual = 100% visuals
Example of a visual x 100% het = 50% chance of producing visual, 50% chance of producing 100% het
Example of a 100% het x 100% het = 25% chance of producing visual, 75% chance of producing 66% het
Example of 100% het x normal = 100% chance of producing 50% het