FAQ

Het Percentages

A "het" is a heterozygous carrier of a recessive trait. The animal does not show the morph but carries one copy of the allele. The percentage on the het tells you the chance that this specific animal carries.

The three percentages you'll see

  • 100% het — the animal definitely carries. Either it's a non-visual offspring of a visual parent, or it's been DNA-tested.
  • 66% het — the textbook 2/3. Comes from the cross het × het: visual offspring are filtered out, and among the non-visual survivors, 2 out of 3 are carriers.
  • 50% het — the textbook 1/2. Comes from het × normal: among the non-visual offspring, half are carriers.

There's a fourth label some keepers use, "possible het" — that's effectively a 50% het where the parent's status is itself uncertain. The calculator treats it as a 50% chance.

The 66% rule, explained

Cross two Het Albino × Het Albino. The textbook splits offspring into:

  • 25% visual Albino
  • 50% het carrier
  • 25% wild-type, no copies

At hatch, the het and the wild-type babies look identical. You only know they're not visual. Of the 75% non-visual fraction, two-thirds are carriers and one-third aren't:

Out of the 75 non-visual babies, 50 are carriers and 25 aren't. So 50 ÷ 75 = 0.6666… — about 2 in 3.

That's where the 66% comes from. Every non-visual hatchling from a het × het cross is recorded as a "66% Het Albino" — meaning we don't know which of the 75% it is, but there's a 2-out-of-3 chance it carries.

Why 66% and not 67%

0.6666… rounded the strict way is 67%, not 66%. So why does the app show 66?

The breeder community has used "66% Het" for decades. It's the convention on every classified ad, every sticker on a tub at a show, every breeder's listing on MorphMarket. Showing 67% would make the calculator's output look unfamiliar even though the math is the same — and it would mismatch what gets printed on the QR-coded labels people are taking home.

The calculator deliberately rounds down, not to the nearest. The textbook 2/3 case lands on 66%, matching the convention. The same rule applies everywhere — when you record a "66% Het Albino" hatchling via the Record Hatching dialog, the app saves 66, not 67.

That's a deliberate choice between strict math rounding and the working language of the hobby. The hobby wins.

The 50% case

A Het × Normal cross gives 50% het and 50% normal. Among the non-visual offspring (which is everyone here, since neither parent is visual), exactly half carry — a flat 50% het.

Same idea as the 66% case, just simpler arithmetic.

When the rule doesn't apply

If one parent is visual and the other is het, every non-visual baby is definitely a carrier — the visual parent always passes a copy. Those offspring are recorded as 100% het, not 50% or 66%. The calculator skips the rule when no wild-type can come out of the cross.

In short: het percentages are a way to be honest about what you can't tell apart at hatch. They're not a fudge — they're the actual chances given what's visible.

Het 100% is also a thing — and it's earned

A 100% het comes from breeding back. Take a visual Albino, cross to a normal — every baby is a 100% het, because the visual parent gave them all a copy. Take that 100% het, cross to another visual — half of those babies are visual, the other half are 100% hets. And so on.

Some keepers prove out hets by breeding the suspected het to a visual or another suspected het and seeing if any visuals appear. If any visual hatches, the suspected het is confirmed as a carrier. If a meaningful number of clutches yield zero visuals from a "66% het" pairing, it's evidence the suspected het was actually wild-type — and you can adjust the recorded probability down (or remove the het entirely) on the animal page.