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Royal Python Genetics

Royal Pythons are available in hundreds of different colours and patterns from a solid white snake with blue eyes, to bright yellow, stripey, purple and even jet black. Royal Python breeding kicked off in the hobby in the 1990's - early 2000's with many breeders importing direct from West Africa, spotting differences in patterns, breeding to their collection creating new morphs, or heterozygous animals to breed back to create recessive morphs. As this was such a success, the Royal Python is now one of the most popular reptiles to keep in captivity due to their wide variety.

This page will cover the basic terminology needed to understand how genetics work,  how to use the Punnett Square so you can calculate the outcome of your breeding projects and address some of the problematic genes and combinations that can occur when breeding.


There are a few commonly used words used in the hobby, and here we will give you an explanation as to what they mean:

  • Gene - Genes are molecular units of DNA responsible for the physical and inheritable characteristics of an animal.
  • Chromosome - Chromosomes are where genes reside. A royal python contains 18 pairs of chromosomes (36 in total). 18 will be inherited from the mother, and 18 will be inherited from the father, all containing the genetic make up of the parent snakes.
  • Locus - A locus is the fixed location on a chromosome that a specific gene resides. There are thousands of loci per chromosome, all containing different genes that contribute to making a specific part, trait, or appearance of an animal.
  • Alleles - An allele is basically a different version of a gene. If two animals share this allele, the physical traits will be present.
  • Heterozygous - Heterozygous (het) is the term used when referring to an animal which carries a gene, but doesn't show any physical evidence.
  • Homozygous - Homozygous is the term used for an animal which shows the physical traits of a gene.


Dominant genes are a visible mutation, and only requires one copy of the gene to be visual (Homozygous). Unlike the incomplete dominant genes, Dominant genes don't have a super version, even if the alleles are paired, There are only a few Dominant genes including the Wild/Classic type, Spider and Pinstripe.

Co-Dominant (Incomplete Dominant)

An incomplete dominant morph, or more commonly know as co-dominant morph is a snake that looks different to normal (dominant), yet only requires on copy of the gene. Also, the incomplete dominant morphs have a super version. This is present when the allele for that gene is paired. These morphs are known as super versions. Examples of incomplete dominant genes are Pastel, Mojave, Banana, Cinnamon, Black Pastel and Lesser.


Recessive morphs are generally the most difficult to produce. These snakes require a copy of the gene from both parents for a visual representation (Homozygous). Piebald, Albino, Genetic Stripe and Clown are a few examples of recessive genes.

How to use the Punnett Square

The punnett square is a basic mathematical model used to work out the percentage chance of the outcome based on the parent animals. This is the easiest and simplest way to understand your possible offspring when deciding which animals to pair for breeding. Below we will show you how to construct and use the punnett square, apply your genetics, and understand the outcome. For this first example we will use a very basic pairing, and more complexed pairings will be listed below.

Step 1.

First, we need to allocate an ID to each parent. For the Banana we use "BN" to indicate that this possesses one copy of the Banana gene, and one copy of the Normal gene. For the Normal, we use "NN" as this contains two copies of the Normal gene only. We then use this information to construct the punnett square.

Step 2.

Now we've given our parents an identification, we now allocate this pair of letters to their own location at the punnett square. Parent 1's genetic identification is positioned at the the top, and parent 2's genetic identification is positioned to the left. 

Step 3.

Now this is where the magic happens. An allele form Parent 1, and an allele from parent 2 are re-positioned to make a new pair within the punnett square. As we can see, the top square takes a "B" from Parent 1, and an "N" from parent 2. This tells us that this pairing of the alleles will result in a Banana offspring as the incomplete dominant genes only need one copy to have a visual expression.

Step 4.

Let's now fill in the remainder of the punnett square using the method displayed in step 3. All four of the the squares will inherit one gene from parent 1, and another from parent 2.

Step 5.

Lets take a look at the results. We can see that half of the squares are filled with "NB", and half of the square is filled with "NN". This means that there is a 50% chance of producing "BN" (Banana), and 50% chance of producing "NN" (Normal).

Step 6.

Now we can see the percentages as a result of using the punnett square, it is key to understand that these are purely percentage chances. On average, a clutch of 4 eggs will result in 2 Banana and 2 Normal, As these are percentage chances, this type of result isn't always the case. The example used above could result in 4 Banana, and no Normal (which could be considered a great result), but the same clutch could result in 4 Normal and no Banana (almost always considered a negative result). The percentage chance will always be the same regardless of the number of eggs in the clutch.

Recessive x Dominant

As you can see, this pairing results in all offspring having the same genetic make up. All offspring will have the visual appearance of a Normal due to this being the dominant gene, but all offspring will also be heterozygous for Piebald. This means that they have one copy of the recessive gene, but as we know, two copies of the recessive gene are required to make it a visual trait.

Recessive x Dominant (Heterozygous)

This pairing works slightly different to the Recessive x Dominant as the dominant animal here is heterozygous for Piebald. Using the punnett square, you can see that the results are different. 50% of the offspring now have a chance of being a visual Piebald, and 50% will be heterozygous for Piebald.

Recessive x Recessive

A recessive x recessive pairing guarantees 100% recessive offspring. As both parents possess a pair genes for Piebald, all offspring will inherit a pair of genes for Piebald. There are no other possible outcomes to this pairing unless there are other genes involved.

Incomplete Dominant (Co-Dominant) x Dominant

This pairing basically works like a Dominant x Dominant, however because the incomplete dominant animals only need one copy of the gene, visual traits will be present if it is passed to the offspring. As you can see, 50% of the offspring will be Banana, and 50% of the offspring will be Normal. In this case, the Normal animals won't be heterozygous for Banana as the incomplete dominant genes are homozygous. Basically, if it doesn't look like a Banana, it isn't, nor does it carry any of those genes.

Incomplete Dominant x Incomplete Dominant

This pairing is the most popular way to create combos as only one copy of the incomplete dominant gene is needed for an expression. As you can see, this pairing has four different results, a 25% chance of creating single gene animals (Banana or Pastel), an animal with a combination of genes (Banana and Pastel), and a Normal wild type.

Problematic Genes & Combinations

There are a few genetics to approach with caution when choosing to breed Royal Pythons. Some genetics and genetic combinations can cause physical and neurological defects, and few can be fatal. Here is a list of the genetics to be aware of and their effects…


Probably one of the most well know genes to present a neurological defect in Royal Pythons. The Spider gene was one of the earliest “morphs” to be introduced into the hobby. The Spider gene can make fantastic combinations, but often lead to neurological issues. All specimens the contain the Spider gene 100% possess the neurological defect, but the degree of presentation seems to be “random”. Some snakes will exhibit very little signs of this defect, whilst for others it can be debilitating.


Head wobble is the most obvious sign, and this effect can vary significantly from one specimen to another. Snakes with little head wobble generally live out the lives of any other normal Royal Python, however, snakes with severe head wobble can struggle to strike at their food accurately and eat, and this can be a stressful condition for you snake to endure. Snakes with severe head wobble often also “cork-screw”. This is where the snake raises its head in an upward spiral motion, and struggles to understand which way is up, and which way is down… almost as if it has lost all balance.


Breeding the Spider x Spider is almost always fatal. Young don’t generally develop fully, and those that do often don’t make it out of the egg. Breeding Spider x Champagne has the same result.



The champagne gene is another beautiful morph and again, creates some amazing combinations. The champagne gene is very similar to the Spider gene in that some specimens can present some degree of head wobble, but this is not always the case. Unlike the Spider gene, the neurological defect isn’t always present, and the effects aren’t generally as severe, however some animals can be affected to the same degree as the Spider gene, but this isn’t very common.


Breeding Champagne x Champagne, or Champagne x Spider is almost always fatal. Young don’t generally develop fully, and those that do often don’t make it out of the egg. Champagne has a number of incompatible genes such as Spotnose which can enhance the severity of the head wobble, but also add physical deformities such as kinking of the spine. Hidden Gene Woma is another incompatible gene often resulting severe head wobble.


Cinnamon / Black Pastel

Cinnamon and Black Pastel are two great genes for creating dark morphs, however caution should be applied when mixing two of the same genes together, or a combination of them both.


The Cinnamon and Black Pastel genes are basically two separate lines of the same gene. These are allelic, and the results of mixing them results in a solid black snake. The same result can be achieved by combining two copies of the same gene also.


There are two main physical defects that can occur with this genetic combination. Kinked spines are the most common and serious of the two, but again, the severity of this defect can vary. Specimens can hatch out of the egg with no problems if the kinked spine isn’t too large or deforming. Kinks below the cloaca doesn’t usually cause any issues at all. Some specimens can also appear to be fine with small kinks above the cloaca, but the observation is important as the deformed internal structure can affect feeding, digestion, and defecation. If large kinks are present, regardless of position, young often fail to hatch out of the egg.


The second physical defect related to this genetic combination is “Duckbilling”. This defect often causes the snake to have an overbite or wider mouth than a normal specimen. From our experience, this defect doesn’t seem to have a detrimental effect on the snake’s wellbeing, and most will eat with no issues.



The Lesser gene again is one of the earliest morphs to be introduced to the hobby, and adding this to certain combinations can produce some stunning offspring.


The Lesser gene can also be used to produce the Blue Eyed Leucistic morph, resulting in an all-white snake with blue eyes, however this can also lead to another physical defect. Lesser x Lesser pairings that produce Blue Eyed Leucistic animals can be subject to a defect know as “bug eyes”. The eyes on a BEL produced by a Lesser x Lesser pairing can sometimes be larger than a normal specimen. There is very little evidence that this defect hinders the animal’s health or wellbeing, but it can make the snake look a little odd.


There are other ways to produce Blue Eyed Leucistic snakes with little chance of physical defects such as Mojave x Mojave, Het Russo x Het Russo, Phantom x Phantom or any combination of those genes. Some BEL animals can have cleaner whites than others depending on the pairing chosen.



Desert is another fantastic gene to introduce into combinations, but again, this can be problematic depending on how you choose to reproduce animals containing the Desert gene. Female specimens are "infertile", and a s far as we know, there is yet to be a viable clutch produced. Technically they aren't infertile because they can actually build follicles and lay clutches of eggs, but more often than not, the eggs will be slugs. Laying a clutch of slugs is probably the best scenario if you choose to breed a female Desert Royal Python.

The more serious alternative to laying slugs would be the female becoming egg bound. This is when the female produces follicles, proceeds through an ovulation, but cannot part with her eggs, thus causing her to become egg bound. Egg binding is a very serious issue and can be fatal to any snake, regardless of breeding weight and size. Surgical intervention is generally needed if egg binding occurs.

Why does this happen you ask? Well, to be honest, no one really knows, but there is some evidence stating that when the fertilised eggs are fully developed, they begin adhering themselves to the lining of the uterus, thus leaving your female unable to pass the eggs.