A recessive trait is only visible when an animal is homozygous for said trait, meaning it must inherit the gene from both parents. This is why breeding, say, an albino to a normal will produce all normal appearing offspring. They will only receive the recessive albino gene from the albino parent. They will, however, all carry the gene, making them 100% heterozygous for the trait.
So how does one reproduce a recessive morph? There are several ways…
Let’s start with the most obvious, and for simplicity’s sake, we will continue to use the albino morph for our examples. The methods and stats would be the same for any recessive morph though (axanthic, clown, piebald, caramel, etc…). If you breed two albinos together, all resulting offspring will be albino. Why? Because all homozygous animals pass their gene for that morph on to all of their offspring. If both parents are albino, each of the offspring will receive one gene for albinism from each parent, making them homozygous for the trait (i.e. albino). Slam dunk, every baby, every time.
Now we are going to get some hets involved… Say we have an albino male. As stated above, he is going to pass that gene on to 100% of his offspring 100% of the time. Now an animal that is heterozygous for a morph passes that gene on to approximately half of its offspring. So when we breed the albino male to a het female, all of the babies are guaranteed to get the gene for albinism from the father, but only half (statistically) will get the gene from the mother. The babies that get the gene from both parents (homozygous) will be albino. The remaining half of the clutch will appear normal, but will have the gene, making them heterozygous (100% hets). This is where the term 100% hets comes from- When a baby python has a parent that is albino, even if the other parent is normal, it is 100% guaranteed to be heterozygous for the trait.
So what’s a “% possible” het? Let me start by saying what it isn’t. It isn’t an animal that is het, but in some way “less” het than a 100%er. An animal is either a het, or it isn’t. The number refers to the statistical likelihood of the animal being het based on the parentage, but since het and non-het offspring appear the same, the only way to know for sure is to raise the animal up to adulthood and breed them to another animal with the gene in question. I think the confusion comes from the occasional dropping of the key word- possible. Sometimes you see an animal listed as a 66% het, as opposed to a 66% possible het, leading one to believe that they are some sort of lesser form of het. I can’t stress this enough- An animal is either a het, or it isn’t! Now lets talk about where possible hets and the numbers associated with them come from.
Let’s take a 100% het male crossed with a 100% het female. Out of a theoretical 4 offspring, one will get the gene from both parents (making it albino), two will get the gene from one parent but not the other (making them het albino), and one will miss the gene all together (making it normal). Since the three that are not albino all appear normal, however, one can not determine which ones are hets and which are not. This is why they are referred to as 66% possible hets- 66% is the equivalent of 2/3, or 2 out of 3. Remember, these are statistical likelihoods – not guarantees. You can breed a pair of 100% hets together and produce all albinos, some albinos, or even no albinos! As for the normal appearing offspring, some may be hets, all may be hets, or none may be hets. That’s why we use the numbers. It gives us a way to determine approximately how likely an animal is to have a gene that it isn’t showing, which is helpful in both determining price as well as whether or not a keeper wants to invest the time required to raise the animal to adulthood and “prove it out”.
So where do 50% hets come in? When a 100% het is bred with a normal (or any other animal that isn’t carrying the gene in question- we will stick with the albino trait), none of the offspring will turn out homozygous. Instead, they will have a 50% chance of inheriting the gene from the heterozygous parent. If they do inherit the gene, they will be het for the trait only, but again, since you can’t tell the normals from the hets we call all of the offspring 50% possible hets. Again, it bears repeating- the offspring, individually, either are hets or they aren’t. They aren’t “half hets” or anything of the sort. You have to raise them and breed them, potentially for many seasons, to know with any certainty. If, however, you breed a possible het albino to either an albino or a het albino, and you produce even one albino baby, your possible het just became a 100% het!
Here’s one other term you may see occasionally. It’s one I use only in my personal notes, but not in listings of animals for sale in general- 33% or 25% possible het. I use this as a short hand way of noting that an animal has an unproven possible het parent. An example would be the offspring of my 2005 pastel, who is also a 50% possible het ghost. I refer to his progeny as “25% possible het ghosts”. Should I prove him out to be heterozygous for the ghost morph, his offspring will all be upgraded to 50% possible het ghosts. I just split the parents statistical percentage of carrying the gene in half, so at a glance I know there is a chance that another gene is hiding in there. It isn’t an accurate statistical likelyhood, just a way of keeping tabs on all the genes that could be in play.
If you can wrap your head around this, then co-dominant and dominant morphs will be easy for you to understand. The statistics are all the same, but the hets are visible, making it a lot easier to know what you are producing. There are rare instances in recessive morphs where hets may show certain characteristics making it easier to pick them out from their siblings (such as het pied “markers”) but they aren’t 100% reliable in general. The only sure way to prove anything is with patience, hard work, and a lot of breeding. That’s what makes recessive morphs more valuable than their co-dom counterparts (in general), and also that much more rewarding to produce!