Reptile morph calculator
Pick the genes each parent carries and see exactly what the pairing can produce — per gene and per combination. No account, nothing installed, nothing stored.
Sire (male)
Which genes the father carries, and in what form.
No genes yet — this parent is treated as a normal animal.
Dam (female)
Which genes the mother carries. Sex matters only for sex-linked genes.
No genes yet — this parent is treated as a normal animal.
Add at least one gene to a parent to see the predicted offspring.
What this calculator models that most do not
Simple recessive and co-dominant genes are easy, and every calculator gets them right. The interesting cases are the ones where a textbook Punnett square quietly gives the wrong answer, and those are the ones that cost breeders a season.
- Allelic series — genes sharing a locus, which can never be inherited independently or stacked as separate supers
- Compound hets — one allele of each at a shared locus, which shows as its own morph rather than as a carrier
- Lethal super forms — the non-viable class is dropped and the surviving odds renormalised, so Spider × Spider reads about 67/33 rather than 25/50/25
- Sex-linked (ZW) genes, split into sons and daughters instead of averaged into one misleading figure
- Possible hets carried at their real probability, so a 66% het is not treated as a proven one
- Polygenic traits, which are named and then explicitly not given odds
Calculators by species
Each species page opens the calculator with that species selected, alongside the full published gene table and what makes its genetics distinctive.
Common questions
Is the morph calculator free?
Yes, entirely. No account, no sign-up and no limit on how many pairings you try. It runs in your browser — nothing you enter is sent anywhere or stored.
What makes this different from other morph calculators?
It models the three things that break a standard Punnett square: allelic genes that share a locus and can never be inherited independently, lethal super forms where a quarter of the clutch never hatches and the survivors' odds are renormalised, and sex-linked genes that are inherited differently by sons and daughters. It also refuses to put a percentage on a polygenic trait rather than inventing one.
Does it handle possible hets?
Yes. Choose 'possible het' and set 66%, 50% or 25%, and that probability is carried through the whole calculation rather than being rounded to a het.
Why does it ask which parent is the sire?
Only for sex-linked genes. Snakes use a ZW system where the male carries two Z chromosomes, so a sex-linked gene is inherited differently depending on which parent has it. For every other gene it makes no difference which animal you put on which side.
Can I save a pairing?
Not on this page — it is deliberately stateless. A HerpSync workspace runs the same engine against your own recorded animals, so you pick two records instead of ticking genes, and the pairing, its clutch and the actual outcome are all kept.
Run the same engine against your own animals
Record genotypes per animal and every pairing prediction comes from real records — plus pedigrees, inbreeding coefficients and what each clutch actually produced.
Get started free