The Most Extensive Collection of Ball Python Mutations in Captivity

NERD Herpetocultural Library

Simple Recessive Genetics 101

At this point we'll assume that you've already read our Intro to Reptile Genetics page & are somewhat familiar with the terms we'll be using going forward. Most of the genetic terms on this page are "clickable" and will bounce you back to the glossary page if you need to refresh your memory.

General Information

Simple Recessive Genes - what are they and what do they do?

Simple recessive traits are proven, inheritable genes that are only visible in their homozygous form. When a homozygous animal is bred to a wild type (normal), non-gene-carrying animal, all of their resulting offspring will be normal in appearance, but will carry the gene from the homozygous parent. This is due to a mutated allele being passed on from the homozygous parent to the offspring, and a normal allele being passed on by the wild type parent. Since the two alleles are different, they dictate that the offspring's phenotype will be normal, while their genotype is heterozygous. These offspring are known as "heterozygous" or simply "hets." To reiterate, the offspring carry a genetic code for the mutation but are not visibly different from a normal, or wild type, animal.

Examples of Simple Recessive Traits in Reptiles

The following is a list of genetic mutations in reptiles that have been bred & proven simple recessive. This list is not all-inclusive, but intended to give an idea of simple recessive genes and their frequency in the herp world, as well as some of the popular species in which they are commonly found.

Ball Pythons
Corn Snakes
Burmese Pythons
Reticulated Pythons
Leopard Geckos
Albino (T-) Albino Albino Albino Albino
Axanthic Anerythristic Granite Calico Blizzard
Caramel Albino Bloodred Labyrinth Caramel Albino Carrot Tail
Clown Candy Cane Patternless Striped High Yellow
Genetic Stripe Caramel     Hypomelanistic
Ghost Hypo Hypo     Jungle
Lavender Albino Motley     Patternless
Leucistic Striped     Tangerine
Piebald And more!     And more!
Punnett Squares for Simple Recessive Genes
Note: While we use albino ball pythons as our example here, the following punnet squares apply to any simple recessive mutations in any species.
Normal X Homozygous Parents    

Here we'll demonstrate a punnett square to show the resulting offspring from breeding a Normal/wild type ball python (NN) to an Albino ball python (aa).

As we can see from the above square, all of the offspring from breeding a Normal to an Albino will be normal in appearance, but carry the gene for albinism (Na). The offspring are all 100% heterozygous (Na) for albino, otherwise known as "definite hets."

Normal X Heterozygous Parents    

This punnett square shows the offspring from breeding a 100% heterozygous for albino (Na) ball python to a Normal/wild type (NN) ball python.

From this pairing of heterozygous (Na) to Normal (NN), we can see that all of the offspring will be normal in appearance, but half of them will be heterozygous for albino (Na). Breeding hets to normals produces what are known as "50% possible hets." Since half of the offspring are hets, but all of them are normal in appearance, you have a 50% chance of the animal you pick from that clutch actually being a heterozygous (Na) animal. The fastest way to prove which of the offspring are definite hets (Na) is to breed them back to a homozygous (aa) animal. If the animal you picked was one of the definite hets, then you should theoretically see a homozygous (aa) animal (in this case, an albino) in their offspring.

Heterozygous X Heterozygous Parents    

Moving on to our next genetic combination, we have a punnett square for the results from a het for albino (Na) ball python to het for albino (Na) ball python breeding.

Out of the four offspring shown in this square, we see one normal/wild-type/non-gene-carrying animal (NN), two heterozygous animals (Na), and one albino (aa) animal. Just like with the normal-to-het breeding shown above, the two hets (Na) and one wild type (NN) snakes from this pairing are all normal in appearance, so it is impossible to tell which animals are the hets. Since approximately 2/3 (or 66%) of the normal appearing offspring in this clutch are actual hets for albino, they are labeled as "66% possible hets."

As we can see here, breeding hets together can be a very feasible way to produce a homozygous animal. Hets are a great way to get into some of the higher-end projects, since they're typically much less expensive than the homozygous forms.

Heterozygous X Homozygous Parents    

Here we explore another "instant gratification" combo: breeding a het albino (Na) ball python to an albino (aa) ball python. As we'll see from the punnett square, this pairing produces homozygous animals.

What a great combo this is!! According to our punnett square, out of the four resulting offspring two will be het for albino (Na) and two will be homozygous albinos (aa)! Since one of the parents was a homozygous (aa) animal, all of the normal-appearing offspring will be 100% hets (Na) - no guesswork involved.

Homozygous X Homozygous Parents    

Our final punnett square is very straightforward. Just as two completely normal, wild-type (NN) animals will produce all normal, wild-type (NN) offspring, two homozygous albino (aa) ball pythons bred together will produce all homozygous albino (aa) offspring.

Now that's a great clutch!


Something to keep in mind when dealing with punnett squares and simple recessive genetics is that the numbers involved are theoretical. For example, according to theory, breeding a 100% het-albino (Na) ball to an albino (aa) ball should yield half hets and half albinos out of 4 eggs. It doesn't always work this way though...we've bred hets to homozygous animals and gotten all homozygous, we've also bred hets to homozygous animals and gotten all hets. Depending on how the alleles fall, it's possible to breed two hets together and get all possible hets, or do the same and get all homozygous animals as a result. This can be very exciting or somewhat disappointing, depending on what you were expecting out of the clutch. That's a big reason why it's important to keep these numbers in mind as a hypothetical, best-case-scenario according to the laws of genetics. At the same time, that's what makes working with color morphs both extremely fun and also nerve-wracking!

Ready for more? Visit our Double Heterozygous Genetics 201 or Co-Dominant/Dominant Genetics 301 pages!