Double "D" Reptiles


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Reptile Genetics


On this page, we will attempt to explain and show how genetics in reptiles affects their appearance. Our understanding of this is growing as we read more AND as more captive breeding occurs yearly. What we offer here is a fairly simple explanation. We hope that in the next few months, we will be able to offer even more in an attempt to give more understanding to traits as they appear in reptiles.


Terms Used


Albino - amelanistic - lacking melanin (black pigment)
Anytheristic - lacking red pigment Normal - lacking any genetic traits that are recessive.
Heterozygous - also het. - appearing normal with a recessive traits
Double Hererozygous - also dbl. het. - appearing normal with 2 seperate recessive traits
morph - genetic mutation expressed in the animal's appearance, sometimes referred to as a cultivar
gene - genetic signaler
DNA - dioxyribonucleaic acid - the base material for all living things.

The Basics


When 2 of any animal breed, they send 1/2 of their genetic material, DNA, to the offspring via the sperm (male) and egg (female.) These 2 parts come together in the egg to determine the total outcome of the offspring; sex, color of eyes, skin, size and countless other factors both seen and unseen.

Single traits


We will begin the explanations by looking at a single trait, such as the albino, which is often one of the most common recessive trait seen by individuals looking at reptiles. They will be expressed in the Punnett squares below using the letter "M" for the dominant trait of having melenin and "m" for the recessive trait of lacking melanin. An animal possessing only recessive traits will appear that way (in this case, albino.)

The first case scenario is using 2 totally normal animals. We're posting this to basically show how the traits are expressed using the squares.


In this case, all of the offspring have received a dominant allele from each parent and possess dominant traits with no heterozygous genetic material. Thus, the result for each is expressed using "MM."


In this scenario, since only one of the parents is heterozygous (carries the recessive gene for the desired trait,) the offspring all appear normal since each carries at least one dominant trait ("M".) 2 of the offspring are hererozygous for the recessive trait, albino. These offspring would represent the designation often called 50% possible het for albino.


This configuration shows what happens when 2 heterozygous animals are bred together. Both parent animals carry the recessive gene we are trying to get, but appear normal themselves. (This is a very common way to use less expensive het. animals to obtain the more expensive purely recessive trait appearing animals, such as in ball pythons.) Theoretically, 1 of every 4 offspring will be albino. The others will appear normal with 2 of the remaining 3 being het. This causes the common designation of 66% het. for albino.

1 - normal offspring
2 - normal appearing offspring but het. for the trait
1 - albino offspring


Having one albino and breeding it with a heterozygous animal is a sure way to produce albino and het offspring. This method has been used many times to make certain that a desired trait is obtained, usually in a second generation breeding. As the above figure shows, 1/2 of the offspring would indeed be albino and 1/2 would appear normal but be het. for albino. These het offspring would represent 100%, or guaranteed het., for albino offspring.

2 - normal appearing offspring het for albino
2 - albino offspring

Now, just for the sake of arguement, we'll take a quick look at what happens when 2 animals, sharing the same recessive trait, are bred together. You should have figured the outcome by now, but rest assured, the offspring will all show the desired recessive trait, in this case, being albino.




2 Expressed Traits
In this section, we will be discussing genetic mutations where 2 recessive traits are expressed and how they happen. The most commonly known morph in the herp community is the Snow, most well known in corn snakes but made available in boas in, I believe, 1999. This mutation required the combination of amelanism as well an anytherism. We will explore how each mutation affects the desired outcome and how combining the 2, in all of it's forms can affect this as well.

Our first diagram shows how a genetically normal parent animal and a parent animal that is het. for both traits affect the offspring produced. We will use "A" for amelanistic, or regular albino and "B" for anytheristic, or what has sometimes been termed "black albino."


In this use of Punnett Squares, we can see that, out of 16 possible offspring, 1/2 are genetically normal, and the other 1/2 appear normal but are actually double het. for the desired traits.

In the next drawing, we see how normal appearing parent animals, which are each heterozygous for a different recessive trait, have an impact on the offspring which are produced.


In this instance 1/4 of the offspring are genetically normal (AABB), 1/4 of the offspring are normal appearing but het for amelanistic (AaBB), 1/4 are normal appearing but het for anytheristic (AABb) and 1/4 of the offspring appear normal but are het for both traits, or double heterozygous (AaBb).

The 3rd scenario is using 2 normal appearing parent animals that are both double het. for the 2 recessive traits. If 16 offspring are produced, statistically we should have a 1:16 chance of getting our snow.


Of 16 projected offspring, here are the results that we would typically expect to find.

1 - completely normal animal (AABB)
2 - normal appearing and het for amelanistic (AaBB)
2 - normal appearing and het for anytheristic (AABb)
4 - normal appearing and het for both amelanistic and anytheristic (AaBb)
1 - Purely amelanistic (aaBB)
2 - Amelanistic and het for anytheristic (aaBb)
1 - Purely Anytheristic (AAbb)
2 - Anytheristic and het for amelanistic (Aabb)
1 - Snow - showing the combination of both recessive traits (aabb)

The 4th case scenario using 2 expressed traits is where we have 2 parent animals that express one recessive trait and are each het for the other recessive trait.


1/4 of the offspring appear normal but are double het. (AaBb) 1/4 of the offspring appear amelanistic but are het for anytheristic. (aaBb) 1/4 of the offspring appear anytheristic but are het for amelanistic. (Aabb) 1/4 of the oppspring will be snow. (aabb)

In the case of a snow crossed with a completely normal animal, let us just say that the offspring will all appear normal but be double het for both recessive traits.

In the scenario, let's use a snow, or double het animal and cross it with an animal that has one of the 2 recessive traits but is not heterozygous for the other trait. We won't draw this one out either, but rest assured that the offspring will all appear like the recessive parent and carry the het. gene for the other trait. So, a snow crossed with a pure amelanistic will produce offspring that all appear amelanistic but are heterozygous for anytheristic. The same happens if you switch the 2 traits.

In this last look at 2 traits expressed on seperate genetic markers in the DNA. We'll look at what happens when our snow morph is crossed with either an amelanistic or an anytheristic partner that is heterozygous for the other trait (in the case below we will use amelanistic though the outcome is the same for both.) As you should expect, there will be a high number of snow offspring in such a mating.



As you can see, 1/2 of the offspring will be snow and the other half will be amelanistic and het for anytheristic.

We hope to be able to give you more information in the future regarding genetics. As you can see, this can be a very powerful motivating factor for some people to breed their reptiles, and other animals, in captivity. It provides them an opportunity to work with a portion of science that is available to the "common man." There are countless possible genetic traits that have yet to be worked with and while many have been expressed in one breeding or another, they have not been combined together to see the possible outcome. Because reptiles often mature to reproduce in 1 to 3 years and, usually, there is a fairly large number of offspring to work with in continuing generations, they are a popular animal with which to test many genetic theories.
Watch our home page to see when the next installment of genetic information becomes available on our site.