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Keeping guide 6 min read

Lethal morph combos, species by species

By Tony Gayter ·

The morph pairings that kill, species by species: royal pythons, boas, carpet pythons, retics and two geckos, with how good the evidence is for each one.

Lethal morph combos, species by species
In this guide

Most keepers know royal pythons have a few pairings you don't make. Fewer know the same problem turns up in boas, carpet pythons, reticulated pythons and at least two geckos. I went looking for every one I could find and check, and this is the result, with a note on how sure anyone is about each.

By lethal I mean the animal dies. A wobble, a kinked tail or a tumour is a serious welfare problem, but it's a different one, so those sit in their own paragraphs below.

Almost none of this is in a journal. The only peer-reviewed work covers Spider royals and Lemon Frost leopard geckos, and neither is a lethal combo. Everything I call lethal here comes from breeder reports, hobby issue lists and the Deleterious Gene Policy published by REPTA, the UK trade body. Breeders learned these the hard way and I believe them, but nobody has published clutch counts.

Where the problem belongs to the super, a single-copy animal is not affected. A Champagne is a healthy snake, and so is a Motley boa, a White Out fat-tail or a Lilly White crestie.

Royal python

Three pairings are reported lethal. REPTA lists Super Champagne (Champagne × Champagne) as lethal, with fatal problems in the embryo, and it lists Super Hidden Gene Woma, the animal sold as a Pearl, as lethal too. The third is Champagne × Spider, which is two different genes and so a combo, not a super. Breeders report the babies die in the egg or shortly after hatching. I found no source for that one beyond breeders' own accounts.

Super Spider is still argued over. Many breeders hold that two copies of Spider never survive, which would explain why nobody has shown a proven one. Others have said homozygous Spiders exist and look like ordinary Spiders. I found nothing that settles it. Spider is on REPTA's list either way, for the wobble.

Some royal morphs are on REPTA's list without being lethal. Champagne × Hidden Gene Woma often produces severe neurological problems. Super Black Pastel and Super Cinnamon have an underdeveloped lower jaw and kinked spines and tails. Single-copy Spider has the wobble: two imaging studies found malformed inner ears in every Spider they examined, which is the likely cause, though the two studies looked at only nine Spiders between them.

REPTA also flags Spider × Hidden Gene Woma as a risky pairing, and names Super Spotnose as likely to join the list.

African fat-tailed gecko

Super White Out (White Out × White Out) is lethal. The supers die in the egg or within a few hours of hatching, and no survivor has been reported. People have tried to breed around it and failed. REPTA lists it as lethal.

Carpet python

Super Jaguar (Jaguar × Jaguar) is lethal. Breeders describe a white, patternless baby that dies in the egg or within about a day.

A single-copy Jaguar lives, with a neurological wobble that runs from mild to severe. It's on REPTA's list for that.

Super Zebra is less clear. Two breeders report badly kinked tails and a lot of eggs that don't hatch, but they give no numbers, and live supers exist.

Boa constrictor

Super Motley (Motley × Motley) is born alive and rarely lives past about two years. REPTA describes a metabolic problem: the animal loses muscle tone and can't pass faeces. Keltic × Motley, sold as Smoke, is reported to behave like a Super Motley and end the same way. Breeders assume the two genes sit at the same place, but nobody has shown it.

Super Jungle and Super Aztec shorten or impair the animal's life without killing every one. REPTA lists Super Jungle for poor digestion and fertility problems, and one breeder reports deaths at every age from birth to adulthood, with a handful living past five. Super Aztecs have poor coordination. Some are stillborn or die young and some are infertile, but a minority survive, and at least one is reported to have sired a litter.

Reticulated python

Super Golden Child (Golden Child × Golden Child) is often fatal. Breeders report that many die and that survivors can be small, wobbly or deformed. This is the thinnest evidence on the page, because it traces back to a single hobby list.

Crested gecko

Hobby issue lists call Super Lilly White (Lilly White × Lilly White) fatal. REPTA lists it for defects of the skull, spine, limbs and skin. I wouldn't make the pairing on either account.

REPTA lists Super Cappuccino for the same defects, and I found no report of it being lethal. A Frappuccino carries one copy of each gene and has neither problem.

Welfare problems, but no lethal combo I could find

Lemon Frost is the best-studied morph in the hobby. Super Lemon Frost leopard geckos hatch in the numbers you'd expect, so nothing suggests they die in the egg. In one breeding colony, though, more than 80% of animals carrying the gene grew skin tumours between about six months and five years old. Enigma, also a leopard gecko morph, causes balance and coordination problems. Both are on REPTA's list.

So is Skullface in western hognoses, for a malformed skull, jaw, eyes and nose, and Silkback in bearded dragons, for fragile skin, burns and dehydration.

Where I found nothing I could check

Corn snakes, blue-tongued skinks, gargoyle geckos, kingsnakes and Burmese pythons. They may well have lethal combos. Nothing I found for them stood up to checking, so I've left them off. If you've produced or seen one, tell me and I'll add it.

Sources

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