Understanding Reptile Genetics

Reptile genetics can seem confusing and intimidating, especially when you first encounter terms such as recessive, dominant, codominant, het, polygenic and polymorphic. With so many different terms and breeding possibilities, it can be difficult to know exactly what they mean and how they apply to the reptiles we keep.

 

The aim of this article is to make reptile genetics easy to understand. We’ll break down the different types of inheritance, explain the terminology commonly used by reptile keepers and breeders, and look at how genetics influences the colours, patterns and traits we see in our reptiles. Whether you’re completely new to reptile genetics or simply want to refresh your knowledge, we hope this guide makes the subject a little less intimidating.

 

Types of Reptile Morphs & Colour Variations

There are several different ways that colour and pattern traits can be inherited or developed in reptiles. Some are controlled by a single gene and can be predicted relatively easily, while others involve multiple genes or naturally occurring variation and can produce much less predictable results.

Below are the main categories you are likely to encounter when working with reptile genetics.

 

1.         Recessive Morphs

Recessive morphs are some of the most common and easiest types of reptile genetics to understand once you know what a visual and a het are.

A recessive trait requires two copies of the gene for the animal to visually display the morph. An animal carrying only one copy will look like a normal animal, but it can pass that gene on to its offspring. This is called being heterozygous, or het.

For example, a snake can be visually normal while being a 100% het for a particular recessive morph.

 The most important thing to understand is that a percentage such as 50% het or 66% het describes the probability that an animal carries the gene. It does not mean that the animal is “half het” or “two-thirds het”. Genetically, the animal either carries the gene or it doesn’t. The percentage simply tells us how confident we can be based on its parents and breeding history.

 Some examples in ball pythons include:

-Albino

-Pied

-Clown

 

Let me explain some pairings regarding recessive morphs to paint a full picture.

 

Visual x Visual

All offspring will receive two copies of the recessive morph and thus all will display the same morph.

 

Visual x Normal

All offspring will receive only one copy of the recessive morph and thus will not display the morph, but will have a 100% chance of carrying the genetic. These offspring are known as 100% hets.

 

Het x Normal

Because a het carries one copy of the recessive gene, and the normal carries none, each offspring will have a 50% chance of receiving the gene from the het parent. Thus cresting 50% possible hets.

 

Het x Het

This is one of the most important pairings to understand. Both parents carry one copy of the recessive gene, and therefore each parent has a 50% chance of passing the gene on to an offspring.

The expected outcome is

-25% Visual

-50% Het

-25% Normal / Non-carrier

 

There is a 1 in 4 chance of producing a visual with every offspring. All the non-visual offspring will look the same and generally there is no way to differentiate between hets and non-carriers. Which means the normal looking offspring from such a pairing will be 66% possible hets.

 

Please keep in mind that percentages are odds, not guarantees. For example, if a pairing has a 25% chance of producing a visual recessive that does not mean 1 out of evert 4 babies will be visual. Each offspring represents another independent genetic event. Which essentially means you could have a clutch of 4 offspring and each offspring will have an independent 25% chance to be a visual.

 

Pictured is a Banana Pied Ball Python. Pied being recessive and banana dominant.

 

2.         Dominant Morphs

Dominant morphs are traits where only one copy of the gene is enough for an animal to visually display the morph. This makes dominant traits relatively straightforward compared to recessive genetics. A dominant animal does not carry the gene hidden in the same way a recessive het does, if it has the dominant allele – the trait will normally be visible.

Some examples in ball pythons include:

-Spider

-Pinstripe

-Spotnose

 

 Let's look at some pairings to further understand this genetic.

 

Visual Dominant x Normal

The visual dominant parent has one copy of the gene, while the normal has none. Which means every offspring has a 50% chance of inheriting the dominant gene. So the expected outcome will be half normals, half visual dominant animals. The normals will not carry the genetic in the same way recessive hets do.

 

Visual Dominant x Visual Dominant

Unlike with recessive morphs, just because both parents display the gene does not mean 100% of the offspring will inherit it. Generally, the odds will be 75% visual and 25% normal offspring. But again, the percentages describe expected probabilities for each offspring and are not guaranteed clutch ratios.

 

3.         Co-Dominant / Incomplete Dominant

This genetic has similarities to Dominant morphs and tends to work the same, but with one major distinction. When the offspring inherits two copies of the genetic it will display a visual ‘’Super’’ form of the morph, which is generally more extreme than the visual base co-dominant morph.

 

To see the base trait the offspring only need to receive one copy of the gene to display it. Similar to dominant morphs.

 

Some examples in Ball Pythons:

-Pastel/Super pastel

-Fire/Super fire

-Mojave/Blue eye Leucistic

 

Let’s get into the pairings.

 

Normal x Visual Co-Dom

Approximately 50% of the offspring will inherit one copy of the visual co-dom gene and thus will display the morph. The other 50% will be completely normal. Because the normal parent does not carry the gene there is no chance for offspring to inherit two copies of the gene and produce a super form.

 

Visual Co-Dom x Visual Co-Dom

Here we have three possible outcomes now. Since both parents carry the gene and have a chance to pass two copies on to offspring, those said offspring with two copies will display a more intense super form of the genetic. While also producing the base morph and normals alongside. The odds for such a pairing are as follow:

-25% Super form

-50% Base Morph

-25% Normal

 

Super form x Normal

Since a super form carries two copies of the gene it will therefore pass one copy to each offspring, thus meaning 100% of the offspring will display the base Co-Dom morph. Though, one super parent will not pass one two copies of the genetic meaning there will be no visual super forms in this pairing. Nor will there be normals considering all babies inherited one copy of the gene, enough to display the base morph.

 

Super Form x Base Morph

Here each baby will receive one copy of the gene from the super form parent, and 50% could receive another from the base morph parent. Meaning the odds say 50% should be super forms and 50% should be base morphs. No normals since the super form already passes on one copy to each baby.

 

Super Form x Super Form

This pairing is very straightforward, it will produce 100% super forms since all babies will receive two copies of the genetic, one from each parent.

 

However, there are some genetic traits within this complex which display some forms of abnormalities when produced. One such example is the Motley gene in Common Boa’s (Boa imperator). This gene is a base form co-dom, which means when bred together it can create a super form. This super form is considered lethal, with babies who display it having severe muscle development issues or physical deformities and seldom live past a few months old.

 

Pictured is a Hypo 100% het leopard Boa imperator. Hypo being co-dom. 

 

4.         Polygenic

Not all colours and patterns in reptiles are controlled by a single, clearly defined gene such as the three major morph groups. Some traits are polygenic, meaning that multiple genes contribute to the final appearance of the animal.

 

This term is generally used for a specific pattern or colour appearance which has been created through extensive and selective line breeding rather than simply breeding two animals and expecting a relatively predictable percentage of a particular morph.

 

Breeders might select a specific trait like striping for example, and selectively choose offspring from each clutch which displays the desired attribute strongly, and pair it with another such individual. This is repeated with every offspring to produce a stronger appearance of the said attribute.

 

These attributes could be one of many including:

-Colour intensity

-Pattern intensity

-Pattern reduction

-Amount of colour

-Overall visual quality

 

What separates this type of trait from the three main morph groups is that there are no specific odds or guarantees that a specific trait will be reproduced. Offspring can vary drastically within a single pairing. Along with the fact that there is no such thing as a ‘’Polygenic gene”, where as with the other morphs we can identify the particular genetic mutation responsible for the trait. Here, multiple genetic factors contribute to the final phenotype.

 

Pictured is a Copperhead Viper (Agkistrodon contortrix) with a partially striped pattern. This could possibly be replicated, and offspring with similar traits can be selected for future breeding to increase the striped pattern. 

 

5.         Polymorphism

Some reptiles are naturally polymorphic, meaning that individuals of the same species can display a wide variety of colours and patterns.

 

Unlike a traditional single-gene morph, where we can often predict the appearance of offspring from the genetics of the parents, polymorphic reptiles can produce a much wider range of appearances.

 

One of the best examples is the Amazon Tree Boa (Corallus hortulanus).

 

Amazon Tree Boas are naturally extremely variable. Within the species, individuals can be found displaying colours such as:

 

-Orange

-Red

-Yellow

-Brown

-Grey

-Black

-Cream

-Combinations of these colours

-A wide variety of patterns and markings

 

What makes them particularly interesting is that the appearance of the parents does not necessarily tell you exactly what their babies will look like.

 

This is why polymorphic species can be so fascinating to breed. Two parents can produce babies that look dramatically different from one another, and some offspring may not closely resemble either parent’s appearance.

 

Why Does This Happen?

 

The colour and pattern variation seen in polymorphic reptiles can involve many different genetic factors rather than one simple gene determining a particular colour.

 

Each parent passes a combination of genetic information to each offspring, and different combinations can produce different appearances.

 

This means that even within the same clutch, you can sometimes see considerable variation between siblings.

 

Polymorphic vs Polygenic

 

These two terms are often confused because they can occur together, but they describe different things.

 

Polymorphic refers to the visible variation within a species — multiple different colour and pattern forms occur naturally.

 

Polygenic refers to a trait being influenced by multiple genes and being specifically bred to more strongly represent those genes.

 

A polymorphic reptile can therefore have colour variation influenced by multiple genes but is much more random, the two terms are not interchangeable.

 

Natural Variation, Not Necessarily “Morphs”

 

The different colours of an Amazon Tree Boa should not automatically be treated as separate genetic morphs.

 

They are part of the natural colour diversity of the species.

 

This is an important distinction because the reptile hobby often uses the word “morph” very broadly. A reptile can have an unusual or desirable colour without that colour being controlled by a single identifiable mutation.

 

Pictured is a "Chrome Head" Sumatran Short Tail Python, which is a natural occurring polymorphic trait. 

A normal phase Sumatran for comparison.  

 

A great example of polymorphism in a single species is the Amazon tree boa. Found in many different phases and colours. 

 

6.         Locality

Locality is not technically a morph, but it is important to understand when discussing reptile genetics and appearance.

 

A locality animal comes from a particular geographical area or population, and animals from different localities can sometimes look dramatically different even though they belong to the same species. One such example is the Puff Adder (Bitis arietans), where individuals drastically differ dependent on location. Animals in this species found in Kwazulu-Natal often display a black base colour with bright yellow/orange chevrons and plenty of speckling of the same colour, usually with stronger orange around the face. Where as animals from Tanzania are typically more of a yellow base colour, with black, cream or white patterning and even red chevrons. It is important to note that even within one locality there can be much variation.

 

It is important to try and preserve pure localities instead of blindly mixing with other localities. And when it is done it must be done responsibly and in a controlled situation. Similarly to hybridizing species, doing so irresponsibly could jeopardize future bloodlines purity. When such breedings happen animals must not be put on to the market blindly either, and in my opinion should be kept as personal projects when done.

 

In South Africa specifically there are a few good examples of both locality and species hybridization and why it should only be done responsibly.

 

Carpet pythons are a good example, where in todays market (Or before the AIS listing at least) it is basically impossible to find pure or even clean locality animals.

 

This is a common variant of Rinkhals (Hemachatus haemachatus) found in Gauteng. Usually grey with minimal patterning. 

Where as this is the same species, but found in parts of Kwazulu-Natal where this orange banded variety is common. 

 

Conclusion

Reptile genetics can seem complicated, and they can be, but once the basic concepts are understood it becomes much easier to follow. Especially when getting into combination morphs and breeding different morph types together. Understanding the differences between these genetics is key to your knowledge about specific morph breedings.

We hope this guide has made reptile genetics a little less confusing and a lot more approachable. The world of reptile genetics is incredible diverse and there is always more to learn.