100% 66% and 50% hets

100% - one parent is visual
50 %- one parent is het and the other doesn’t carry the gene
66%- both parents are het but the offspring is not visual.


Visual → Visual = Visual
Visual → Normal = 100% Het
Visual → Het = 50/50 mix Visuals and Hets
Het → Het = 25/75 mix Visuals and Hets (66% Het)
Het → Normal = 50% Het

The percentages are based off of how the genes break down in the Punnett square. It really doesn’t mean anything other than unless you bread a visual to a visual there is some percentage that will be het. As you can see from my diagram above the more visuals you have the better the odds and as you introduce hets your percentage of getting visuals goes down and obviously without both parents carrying the gene you won’t get any visuals.


Those numbers are basically the % chance that the snake is a heterozygous (carrying one copy of the trait). So a 100% het pied is guaranteed to be het for piebald, a 66% het has a 66% chance of being het for piebald, etc and so forth. If you buy a snake that is 66% or 50% het, there is only a possibility that the snake in question is carrying that gene


At the end of the day, remember that everything either is, or is not, 100% het for the gene in question. The 50%, 66%, and 100% are the odds or probability that the offspring is carrying the gene. When you use a visual, the het is 100% guaranteed, there is no question. When you use one het parent, there is a 50% probability or 50/50 chance, it will carry the gene. When both parents are het, either may or may not throw the gene, so you get a 66% probability. It’s only once you breed the possible het animal that you either prove that the gene is present or not. If proven, then the animal becomes 100% het. If it does not prove, it is not het at all. This is the same probability for every egg but that doesn’t mean it will always translate to reality. For instance, you may breed a het, and the entire clutch may prove 100% het, or it may be none. It is no different then a codominant gene. I once breed a Yellowbelly to a Normal, so there is a 50% chance of everything being YB. Out of 9 eggs I hit two YBs and one never made it out of the egg due to a wrapped umbilicus. So if that were a het, only 1 animal out of the 8 that survived, would have proved to carry the het gene.


That’s everything I needed to know!! Thanks so much!

Thank you sooo much!!

One more question- What does it make when you breed a 50% or 66% het to a snake that doesn’t carry the gene? What would you call them if you haven’t proved out the parent?

poss het and that’s it. To be honest unless I produced it and its 100% I only say poss het.

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Ok, that makes sense. So it only makes 50% hets? (Just making sure I know exactly what your saying)

if its a 50% het to a non het its like 25% possibility… that’s why its pointless to give them a number. Each egg has half a chance to get the gene (any gene) from each parent. Pastel to normal is a 50/50 chance of a pastel or a normal. Piebald to normal produces all normals but all are 100% het because in order for the one parent to be visual it must carry two copies of the gene.

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Yup! I understand now! Thanks so much!

That only comes into play for extremely rare genes. 66% to a non het is a 33% and 50% to a non het is 25%. Pos het albino green tree pythons were the last less than 50% pos het I’ve seen people take seriously and that was years ago.


To be honest, if I bred a non proven possible het (50% or 66%) to a non het. I wouldn’t even advertise it as any percentage of possible het. I would simply state the pairing and make certain that any purchaser knows the pairing before completing the purchase. Others may not agree, but that is how I choose to market them.


I agree I really only say 100% or pos het… I don’t even use 50% or 66%. I let the buyer know the pairing.

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FYI- I just moved this to ‘All Reptiles’ as this is a useful conversation that is applicable to all herps.


I’ve gotten shouted down for this before, but I’ll say it again: I actually wished we tracked genetic odds more precisely in the hobby. Not really for purposes of the ads (because yeah being 25% het really isn’t worth any extra money) - but for additional info that comes with the snake after purchase or for our own breeding records.

  1. It would be very useful to know even if there was a 10% chance a snake is het, so when that recessive pops up randomly in a collection you could then back-calculate and isolate where all the other hets are likely to be throughout your collection.
  2. If you had 2 similar choices for a pairing and one had a 10% chance to prove out a recessive it could really inform your decision better.
  3. If you bred a 50% het in a pairing possible to produce visuals, but don’t hatch any - then it’s no longer a 50% het, but also not necessarily a normal. Depending on exact pairing and how many eggs hatched you can calculate the updated odds it is a het and make more informed decisions on future pairings.

This is all great info. I had to do a lot of research as I didn’t understand it at first.

I agree, any chance of any gene should be told to the buyer to make it clear. It can really help down the line when your breeding them and think… That doesn’t look like a… What could it be :thinking: :sweat_smile:

Although you have all the info above, here is a video by MC that may help make it clearer:

Also here are some past threads about het percentages that have some additional info:


I tell them there is a possibiliy… I even include the pairing. But if I have possible het or even 100% het I bought I put it to a visual the first year for the best chance to prove it… because I want my animals represented the best I can.


A little off from the original question, but in my pairings I really avoid anything resulting in a poss het. I tend to do my best to pair visuals to 100% hets as often as possible.