Reptile morph genetics, explained properly
Four modes of inheritance, three exceptions that break a standard Punnett square, and the vocabulary the hobby uses for all of it. Written for keepers planning real pairings, with every example drawn from a gene that is really in our dataset.
The guides
Modes of inheritance
Four words do most of the work in reptile genetics, and three of them are routinely used to mean the wrong thing.
Hets & possible hets
The most misunderstood label in the hobby, and the one most likely to be attached to money.
Allelic series & compound hets
Two morphs that occupy the same position on the chromosome behave in a way ordinary Punnett squares get quietly wrong.
Lethal supers & sex-linked genes
Two exceptions that make a standard Punnett square give the wrong answer — one about which animals hatch, one about which sex they are.
The four modes at a glance
Almost every expensive mistake in reptile breeding starts with assuming the wrong mode of inheritance. These are the four, with how many genes of each are in the published dataset.
Recessive
63 genesTwo copies to show
Needs a copy from each parent to be visible. One copy makes a het — an animal that looks normal and carries the gene.
Co-dominant
43 genesOne copy shows, two make a super
One copy changes the animal's appearance; two copies produce a distinct, usually more extreme super form with its own name.
Dominant
13 genesOne copy shows, two look the same
One copy is enough to see the trait, and two copies look no different from one — so there is no super form to breed for.
Polygenic / line-bred
33 genesSelected, not switched on
The result of many genes plus selective breeding. It intensifies over generations and cannot be predicted by a Punnett square.
Genetics by species
The rules are the same everywhere; which of them actually bite depends entirely on the species. Ball pythons hit all three exceptions at once. Corn snakes are almost pure simple recessives. Gargoyle geckos have nothing Mendelian to calculate at all.
Ball Python genetics
The most morph-driven species in herpetoculture, with four allelic complexes, two dominant genes that are lethal in their super form, and one sex-linked gene.
Leopard Gecko genetics
Three separate non-allelic albino lines, several distinct snow genes, and a large set of line-bred traits that no Punnett square can predict.
Corn Snake genetics
Almost entirely simple recessive genetics, which makes the corn snake the species most worth learning inheritance on before you spend money.
Crested Gecko genetics
Overwhelmingly line-bred traits, one famous lethal dominant, and a small handful of genes that behave predictably.
Boa Constrictor genetics
Live-bearing, long-lived, and built on co-dominant genes whose super forms are the point of most projects.
Western Hognose genetics
A small, tidy gene set built around one classic co-dominant — Anaconda, whose super form is the Superconda.
Bearded Dragon genetics
A small gene set with one genuine welfare decision built into it — the Silkback, which is the super form of Leatherback.
Gargoyle Gecko genetics
A species where every recorded trait is line-bred — and where an honest tool says so rather than inventing odds.
Check a pairing for yourself
The calculator models everything these guides describe — allelic loci, compound hets, lethal supers with the survivors renormalised, and sex-linked genes split by offspring sex. It is free, needs no account, and it will refuse to put a number on a polygenic trait.
Common questions
What are the modes of inheritance in reptile morphs?
Four: recessive (needs two copies to be visible), dominant (one copy shows, two look the same), co-dominant (one copy shows and two produce a distinct super form), and polygenic (produced by many genes and intensified by selective breeding, so it cannot be predicted at all).
Why do some pairings not give textbook Punnett square odds?
Three reasons, all common in herpetoculture. Allelic genes share a locus, so they cannot be inherited independently. Some super forms are lethal, so a quarter of the clutch never hatches and the survivors' odds are renormalised. And sex-linked genes are inherited differently by sons and daughters.
Is a morph the same thing as a gene?
Usually not. Most morph names sold at expos are combinations of several genes — a Bumblebee ball python is Pastel plus Spider, and a Snow corn snake is Amelanistic plus Anerythristic. Only the underlying genes are inherited; the combination name is what breeders call that set.
Do I need to pay to use the morph calculator?
No. The morph calculator on herpsync.com is free and needs no account. A HerpSync workspace runs the same engine against your own recorded animals, which is the part that needs a plan.
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