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Odds

When breeding heterozygous to heterozygous animals or even heterozygous to homozygous it's important to remember that the percentages shown in the Punnet's square diagrams are the odds for each egg, not a guarantee of what you will get in any particular 4 or 16 egg clutch.  

Each egg from a heterozygous X heterozygous breeding has a 25% chance of being homozygous and is independent from the 25% chance of the other eggs in the clutch.  

With heterozygous X homozygous breedings, each egg has a 50% chance.  Pretend you have a clutch of 4 such eggs and flip a coin 4 times to see how they come out.  Repeat this a few times and you will see that you will not always get 2 homozygous and two heterozygous as per the square.  Do it enough times and you will eventually get some imaginary clutches with 4 albinos and also some with none.

So, how do you know if you have a het or not if it doesn't produce the expected recessive mutant in the first clutch or two?  Unfortunately, you can never know with absolute certainty.  The best you can do is figure the odds and get a feel for how likely it is that you where just unlucky verses how likely it is that you don't have a het.

Here is a useful formula to figure the odds of getting at least one homozygous egg out of a given number of eggs:

1 - (chance not homozygous)^number of eggs

In a het to het breeding, each egg has a 25% chance of being homozygous and hence a 75% chance of not being homozygous.  If you have a four egg clutch from het X het the chance of producing at least one recessive mutant is:

1 - 0.75^4 = 68%

If you don't produce a mutant, you might just have been the unlucky 32% on this clutch so the odds probably don't justify assuming your hets aren't real hets.

Here are charts showing the odds of producing at least one recessive mutant from various numbers of eggs (assuming all hatch).  It will be up to you to decide how sure is sure enough that you don't have a true het (i.e. if you didn't produce a mutant in enough eggs to have had a 99% chance of producing one do you not have a het or are you the unlucky 1%).

The above chart is for heterozygous X heterozygous as in your chance of producing a recessive albino from crossing two heterozygous albinos.  The below chart would apply to crossing a heterozygous albino to a homozygous (visible) albino.

The Het X Mutant chart could also be used when purchasing 50% chance possible hets since both deal with "50%" odds.  From the chart above you can see that if you randomly pick three 50% possible hets then your chance of having at least one het is 87.5%.

This leads into a discussion on what "randomly pick" means.  All the eggs in a clutch or all the eggs of one gender in a clutch would be a random pick.  Assuming these come from a het male to a normal female there are millions of sperm involved and about half are het and half aren't.  Each egg's conception is statistically independent because there are so many sperm.  If the first egg is fertilized with a heterozygous sperm there are still 999,999 het sperm to 1,000,000 not het sperm so still even odds as to if the next egg will be fertilized by a het sperm or not.  A clutch of four 50% hets is just as likely to not have any hets as flipping a coin 4 times is to come up tails all four times (6.2% chance).

However, if there is no way to identify a het based on appearance, personality, feeding characteristics, or any other way short of breeding it then any selection of 50% chance hatchlings, even across different clutches is a random selection.

The catch is if someone finds a way to pick out the more likely hets before you make your random selection of the remaining possible hets.  This would decrease your odds to less than the expected 50% or 66% per animal.  

Normally you would not expect there to be any outward signs in hets for recessive genes and for years I dismissed all claims from people who said they could tell otherwise.  However, in two Burmese python mutations there is good evidence for sporadic but reliable signs of hets.  These are the Granite and Green mutations.  Some het Granite burms show a puzzle pattern with highly irregular and broken up blotches that are intermediate between normal and granite pattern.  Likewise, some het green burmese pythons have the leopard pattern with wider than normal spaces between the blotches which can be thought of as intermediate between normal and green (a.k.a. striped or patternless).  I don't have a feel for how common these signs are in hets but I know that many hets to not have them at all (I have no explanation for this).  Fortunately these patterns are fairly unique in the burm population so that if you do see them you can be pretty sure you are looking at a het even if all hets don't show them.

Now days whenever I hear of a new pattern mutation in ball pythons I wonder if there could be a sporadic sign seen in some of it's hets.  I have not seen any proof of this in any of the existing mutations but then I haven't seen very many if any for sure hets for most mutations.  The newer a mutation is, the fewer people would be in a situation to notice something like this.  It will be interesting to see how the ball python community handles the situation if evidence starts to mount of a sporadic tell for het.  If you publicize a hunch without enough evidence you could feed unjustified high prices for possible hets with the alleged sign.  On the other hand, if you continue to hold back the ones with the sign after you are pretty sure they are hets you shouldn't be selling the rest as full 50% or 66% chance.