Royal Python Genetics for Absolute Beginners

You've probably started looking at royal pythons for sale and, within about thirty seconds, hit a wall of words that meant nothing. Pastel. Het clown. Super mojave. BEL. Some of these snakes cost more than a used car, which makes it all the more baffling.

It's fine that none of it makes sense yet. Nobody is born knowing this stuff, and the people throwing those terms around were just as lost not long ago.

You don't need a science background for this, you don't need to be "good at biology", and you don't need to be good at maths. There are four ideas to get your head around, and we'll take them one at a time. By the end you'll be able to read a for-sale listing and know what it's telling you.

First: what is a "morph"?

Every royal python carries a set of instructions inside it: its genes. They decide things like what colour it is and what pattern runs down its back. That's true of you, me and every living thing. It's just DNA doing its job.

In the wild in Africa, royal pythons are a fairly ordinary brown and tan. The hobby calls that standard wild version a normal, sometimes wild-type. It's your reference point, the default snake, and it comes up again and again below.

A morph is a royal python that looks different from a normal because of its genes. Brighter colours, a faded-out pattern, unusual eyes, even pure white: those are all morphs. Breeders produced them over many years by pairing snakes that carried particular genes.

Two things are worth knowing before we go on:

1. A morph is genetic. A normal royal python with slightly wonky markings isn't a morph. It's still a normal that looks a bit scruffy.
2. Morphs can be combined. One snake can carry several morph genes at once. That's what's behind long names like "pastel lesser clown". It isn't one exotic thing, it's three genes listed one after another. We'll come back to that once the basics are in place.

And if all you want is a pet: a normal royal python makes a brilliant first snake. It isn't a lesser animal. It's the same species with the same temperament, usually much cheaper and often healthier. If you never own a morph, you've lost nothing. Morphs change how a snake looks, not how good a companion it is.

Second: the three ways a gene can behave

This is the part that matters most. If you only take in one section of this article, make it this one.

Everything starts from one fact: every snake carries two copies of each gene. One copy comes from its mum and one from its dad. Always two.

Whether a morph shows on a snake depends on how that gene behaves, and there are three possibilities.

Dominant. A dominant gene needs only one copy to show. Two copies look exactly the same as one, so there's no "upgraded" version. Pinstripe is the most common dominant morph you'll see in listings.

Incomplete dominant, usually called co-dom in the hobby. One copy already gives a visible change. Two copies give a second, usually more dramatic version called the super form. Pastel is the classic example: one copy gives a brighter snake, and two copies give a super pastel, which is lighter again and looks noticeably different. So when a morph's name includes "super", the snake has two copies of a co-dom gene. Spider is co-dom too, but its super form never hatches (more on that in the welfare section).

Strictly speaking, scientists treat "co-dominant" and "incomplete dominant" as different things. The royal python world uses "co-dom" for the behaviour described here, and as a beginner you can ignore the distinction. What matters is the idea: one copy shows, two copies make a super.

Recessive. This is the one that trips most people up. With only one copy of a recessive gene, a snake shows nothing at all. It looks like a completely standard normal, and you'd never know the gene was there.

You only see a recessive morph when the snake has two copies. Clown, piebald and albino are all recessive. Because the gene can hide, recessive morphs take more planning to breed and often cost more. A plain-looking snake might be carrying something valuable, and the only way to find out is through its parents or its babies.

So: dominant means one copy shows and two look the same; co-dom means one copy shows and two make a super; recessive means one copy hides and two show. That's the hardest part of the article done.

Third: what does "het" mean?

"Het" is everywhere in listings. It sounds technical, but the idea is simple.

Het is short for heterozygous, which here means "carries one copy of a recessive gene".

With a recessive gene, one copy shows nothing. So a snake described as "het clown" looks exactly like a normal brown royal python, but it carries one clown gene. Pair two het clowns and some of their babies will get two copies, and those babies will be clowns.

A few points will save you from tripping up:

• Het only applies to recessive genes. You'll never see "het pastel", because pastel is co-dom: one copy already shows, so nothing is hidden. If someone offers you a "het pastel", they're confused, which makes it a handy test of whether a seller knows their stuff.
• "100% het" means the snake definitely carries the gene, usually because its parents guarantee it. "50% het" and "66% het" are odds: there's a chance the snake carries the gene, but nobody has proven it. A "66% het" doesn't carry two-thirds of a gene. It has a 66% chance of carrying one.
• A het snake looks identical to a normal. It's worth more only for what it might produce, not for how it looks. If you just want a pet, you'd be paying extra for something you may never use.

Fourth: reading a Punnett square

No maths, as promised. A Punnett square looks like homework, but it's a small grid for seeing which babies a pairing can produce. You fill in four boxes and read them. Nothing to calculate.

Here's one for albino, which is recessive. Letters stand for the two versions of the gene:

• Big A is the normal version
• Little a is the albino version

So any snake is one of three combinations:

• AA: a normal carrying nothing
• Aa: het albino (looks normal, carries one albino gene)
• aa: a visible albino (two copies, so it shows)

Now pair two het albinos, Aa × Aa. Each parent passes one of its two letters to each baby at random, like a coin flip. Put one parent's letters along the top and the other's down the side, then fill in each box:

	A	a
A	AA	Aa
a	Aa	aa

Reading the four boxes:

• One box is AA: a normal carrying nothing (1 in 4)
• Two boxes are Aa: het albinos, which look normal but carry the gene (2 in 4)
• One box is aa: a visible albino (1 in 4)

So on average, two het albinos produce about a quarter albino babies, half hets and a quarter plain normals.

The important word is average. These are the odds across a great many eggs, like flipping a coin a hundred times. A single clutch of six might not split neatly at all; you could get lucky, or get no albinos. That isn't the breeder doing anything wrong. It's how chance works, and nobody controls which letter each egg gets.

Every pairing you'll see, however scary the names, is this same grid done once for each gene. Once you can read the four boxes, you can work out any of them.

Why the names get so long

Back to "pastel lesser clown". You now have what you need to read it.

Each word is a separate gene, and each behaves in one of the three ways above:

• Pastel: co-dom, so one copy shows.
• Lesser: also co-dom, one copy shows.
• Clown: recessive, so the snake needs two copies for it to show.

Genes are inherited independently of each other, so pastel doesn't care what clown is doing. A long name is a list of the genes one snake carries. Split it into words, ask how each one behaves, and the listing makes sense.

You don't need to master multi-gene combinations as a beginner; that's for breeders. But a wall of morph names won't stop you in your tracks any more.

Please read this part: welfare

Genetics in this hobby isn't all harmless fun, and a good keeper learns the uncomfortable parts before falling for a photo. This isn't meant to put you off. Most morphs are perfectly healthy, but a few carry real problems, and you should know which.

Spider and "the wobble". This is the most serious one. Spider is a co-dom morph with a web-like pattern, and it's linked to a neurological condition called wobble syndrome. Affected snakes show head tremors and twisting or corkscrewing movements, and can struggle to strike or eat properly. It ranges from barely noticeable to severely debilitating, and there's no way to predict before hatching how badly a snake will be affected. Research on spider morphs found deformities in the inner-ear structures that control balance, and every spider carries some degree of the condition; it can't be bred out while keeping the spider look. The wobble is a defect, not a personality quirk, so please go into this one with your eyes open.

Super forms that don't survive. A super means two copies of a co-dom gene, and for a few genes two copies are fatal. The super spider dies in the egg, which is why there are no living super spiders. The same is true of super champagne and super hidden gene woma, and of combinations of those genes. That's why responsible keepers say never to pair spider to spider or champagne to champagne: a quarter of that clutch is produced only to die.

Supers that survive with deformities. Super cinnamon and super black pastel aren't fatal, but they can produce "duck-billing", a narrowed, misshapen snout, and other deformities such as kinks.

The "designer" hype trap. Rare, expensive combinations get talked up hard, and sometimes the hype ignores welfare. A striking snake with a permanent wobble still has a permanent wobble. When a morph's main selling point is its rarity or price, ask why it's rare, and whether that rarity comes at the animal's expense.

You don't have to memorise every problem gene today. Before you buy or breed anything unusual, spend ten minutes checking whether that morph has known issues. That habit alone puts you ahead of a lot of people.