Genetics Predictor

How Mendelian Genetics Work in Reptiles

Predicting the outcome of a clutch is one of the most exciting parts of reptile breeding. Traits such as Albino, Axanthic, and Piebald in species like Ball Pythons and Leopard Geckos often follow simple Mendelian inheritance. These are commonly referred to as simple recessive traits because the underlying mutation is inherited in a recessive manner.

For an animal to express a recessive trait, it must inherit the recessive allele from both the Sire and the Dam. If it inherits only one recessive allele, the dominant wild-type allele masks its effect, so the animal appears normal. These animals are called heterozygous, or simply hets, because they carry one copy of the recessive allele without displaying the trait.

Genetics Terminology

• Gene: A gene is a section of DNA that contains the instructions for a specific biological function or characteristic. Think of a gene like the category "ice cream flavor." The category itself doesn't tell you which flavor you have, it simply defines what is being described.
• Allele: An allele is a specific version of a gene. Continuing the ice cream analogy, if the gene is "ice cream flavor," then the alleles are the individual flavors such as chocolate, vanilla, or strawberry. In reptile genetics, a pigmentation gene might have a wild-type allele and a recessive albino allele.
• Mutation: A mutation is a change in the DNA sequence that creates a new allele.
• Genotype: A genotype is an animal's genetic makeup for a particular gene, that is, the combination of alleles it inherited. Examples include AA, Aa, and aa.
• Phenotype: A phenotype is the observable physical appearance produced by the genotype. For example, two animals may have different genotypes (AA and Aa) but the same phenotype because both appear normal.

Reading the Genotypes

• Wild Type (AA): The animal has two wild-type (dominant) alleles. It appears normal and does not carry the recessive allele. The animal cannot produce offspring that expresse the recessive trait, regardless of what it's paired to.
• Heterozygous (Aa): The animal has one wild-type allele (A) and one recessive allele (a). It appears normal but carries the recessive allele and has a 50% chance of passing it to each offspring.
• Visual Recessive (aa): The animal has two recessive alleles. It expresses the recessive trait (for example, albinism) and will pass the recessive allele to every offspring.

What is a Punnett Square?

A Punnett square is a simple tool used by biologists and breeders to predict the probability of offspring inheriting particular genotypes. The alleles from one parent are placed across the top of the grid, while the alleles from the other parent are placed down the side. The combinations within the grid show the expected genotypes, and from those, the expected phenotypes for the offspring.

Remember that these percentages represent the probability for each individual egg, not the clutch as a whole. If a Punnett square predicts a 25% chance of producing a visual recessive, every egg has an independent 1-in-4 chance of inheriting that genotype. This means it is possible (though unlikely) to hatch a clutch of 8 eggs and miss the odds entirely, or beat the odds and hatch 8 visuals!

Track Complex Morphs with Clutch Keeper

This calculator handles single-gene recessive traits. But what happens when you start pairing double-het animals or working with incomplete dominant (co-dom) mutations? The math gets complicated rapidly, and keeping track of which hatchlings are "66% Possible Het" vs "100% Het" becomes a logistical nightmare.

Clutch Keeper is a comprehensive breeding application designed to solve this. Input your animals' exact genetics, log your pairings, and let the application automatically generate clutch expectations, track incubation days, and manage hatchling records. Scale your breeding projects with confidence.

Frequently Asked Questions