What 'het' means, and why 66% het is not a discount
The most misunderstood label in the hobby, and the one most likely to be attached to money.
A het is a carrier
Heterozygous means an animal has one copy of a recessive gene and one normal copy. It looks entirely ordinary and it will pass the gene to half its offspring. That is all a het is: an invisible carrier with known parentage.
A het is only ever worth what the paperwork behind it is worth, because nothing about the animal itself shows the gene. This is the one place in herpetoculture where record keeping is literally the product.
Where 66% and 50% come from
A possible het is an animal that might be a carrier, with a percentage attached, and the percentage is not a discount or a confidence level — it is a real probability produced by a specific pairing.
Breed two hets together and you get 25% visual, 50% het and 25% normal. If you then set the visual animals aside, the remaining normal-looking siblings are two hets for every one true normal — so each is a 66% possible het. Breed a het to a normal animal and half the clutch carries the gene, so every baby is a 50% possible het.
- Visual Albino
- 25%
- Het Albino (invisible)
- 50%
- Normal
- 25%
- Of the non-visual siblings…
- 66% are het
Proving out a possible het
You prove a possible het by breeding it to a visual animal of the same gene. If the animal is a het, roughly half the clutch is visual and one visual baby settles it immediately. If it is not, every baby looks normal.
The asymmetry is the trap: one visual hatchling proves the het, but a clutch of normal-looking babies never quite disproves it. Six normal hatchlings from a proving pairing leave about a 1.6% chance the animal is het after all, which is small but not zero.
This is why honest breeders keep the possible-het label until it is genuinely proven, and why a tool should carry the actual probability rather than rounding a 66% into a het.
How HerpSync handles it
A possible het is stored with its own probability, and that probability is carried through the odds calculation for every downstream pairing rather than being treated as a het or dropped. A 66% het bred to a visual gives different numbers than a proven het bred to the same animal, and the calculator shows the difference.
When an animal is proven out, updating the record updates every prediction that depends on it, because the predictions are computed from the genotypes rather than stored.
Double hets and what they are worth
An animal can be het for more than one gene at once — het Albino, het Piebald — usually produced deliberately as a step towards a combination. Double hets look completely normal, and two of them bred together give roughly one in sixteen showing both genes.
Because nothing is visible, a double het is entirely a claim about parentage. Buy them from people whose records you trust, and keep records good enough that yours are worth trusting.
Check it in the calculator
Everything on this page is modelled by the free morph calculator — no account, nothing to install. Pick two parents' genes and it shows the per-gene odds and the full combination table.
Keep reading
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.
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.
Common questions
What does 66% het mean?
It means the animal came from a het × het pairing and did not hatch out visual, so of its normal-looking siblings, two out of three carry the gene. It is a genuine probability derived from the pairing, not a seller's estimate of confidence.
How do I prove out a possible het?
Breed it to a visual animal of the same gene. A single visual hatchling proves the animal is het. A clutch of normal babies makes it unlikely but never impossible — after six normal hatchlings there is still roughly a 1.6% chance it is a carrier.
Is a 50% het worth buying?
It depends entirely on price. A 50% possible het is a coin flip, so it is worth roughly half what a proven het is worth on the same project, minus the seasons you will spend finding out. Buy them priced as the gamble they are.
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