At a glance: A fat tail gecko morph calculator gives the chance of each outcome for one egg, not a guaranteed clutch. It covers two hobby traits, Amel (Albino) and Patternless, both reported as recessive. It cannot predict sex, because incubation temperature sets sex in this species.
A fat tail gecko morph calculator multiplies the odds of each parent passing on a trait to give the chance that a single egg shows it. The African fat-tailed gecko (Hemitheconyx caudicinctus) is a West African species, and captive breeders have built several color and pattern lines from it. Only a few of those lines have inheritance that breeders describe clearly enough to calculate.
This page explains the math, shows worked examples and marks where the numbers stop being reliable. The tool sits below the first section.
What a fat tail gecko morph calculator predicts
The tool handles two traits, listed by their hobby names. Amel (Albino) is reported as recessive, and Patternless is reported as recessive. For both, the label is: hobby name, inheritance reported by breeders, not independently tested.
A recessive trait shows only when an egg receives one copy of the gene from each parent. A gecko with one copy looks normal and is called a heterozygous carrier, or a “het” in hobby language. A gecko with two copies shows the trait, and a gecko with none is a non carrier.
Other African fat-tailed gecko names, such as oreo, zulu, stinger or caramel, are left out of the tool. Their inheritance is unclear, and no published study has tested them. The African fat-tailed gecko morph guide covers what each name means in the hobby.
Morph calculator: choose what each parent carries, then press Calculate.
How recessive inheritance works in this gecko
Each parent carries two copies of a gene and passes one copy to each egg at random. That is why the chances repeat for every egg in every clutch, whatever came before. A pair that produced four normal eggs still has the same odds on the fifth.
The published evidence for recessive albinism comes from a related eublepharid, the leopard gecko (Eublepharis macularius). A 2026 study in the journal Genetics examined the three albino lines in that species (Tremper, Rainwater and Bell) and tied each to a different gene (TYR, SLC24A5 and OCA2). All three were mono locus and recessive.
That is leopard gecko data, and it does not confirm the gene behind any African fat-tailed gecko line.
The lesson carries over in one way. The same look can come from different genes, so two “albino” geckos from different lines may not produce albino eggs together. Where a pairing matters, buy from a seller who can document the line.
Traits that breeders call dominant or line bred do not follow the simple rules used here. The morph genetics guide explains those modes and why a Punnett square fits only single gene traits.
Worked Punnett examples
In the tables, A is the normal gene and a is the recessive Amel (Albino) gene. The same math applies to Patternless.
Chances are per egg, and Amel (Albino) is a hobby name, inheritance reported by breeders, not independently tested.
Example 1: het by het
| Parent 1 gives | Parent 2 gives A | Parent 2 gives a |
|---|---|---|
| A | AA, normal, 25% | Aa, het, 25% |
| a | Aa, het, 25% | aa, Amel (Albino), 25% |
Two carriers give 25% Amel (Albino), 50% het and 25% non carrier. Of the eggs that look normal, two thirds are carriers.
Example 2: Amel (Albino) by het
| Parent 1 gives | Parent 2 gives A | Parent 2 gives a |
|---|---|---|
| a | Aa, het, 25% | aa, Amel (Albino), 25% |
| a | Aa, het, 25% | aa, Amel (Albino), 25% |
The result is 50% Amel (Albino) and 50% het. Every normal looking hatchling is a carrier.
Example 3: het by non carrier
| Parent 1 gives | Parent 2 gives A | Parent 2 gives A |
|---|---|---|
| A | AA, normal, 25% | AA, normal, 25% |
| a | Aa, het, 25% | Aa, het, 25% |
No egg shows the trait. Half the eggs carry it, but nothing visible tells you which ones.
Two traits at once
If Amel (Albino) and Patternless sit on separate genes, which breeders report but no study has tested, each trait is calculated on its own and the results are multiplied. Two parents that are het for both give the outcomes below.
| Outcome per egg | Chance |
|---|---|
| Shows neither trait | 9 in 16 (56%) |
| Amel (Albino) only | 3 in 16 (19%) |
| Patternless only | 3 in 16 (19%) |
| Both traits | 1 in 16 (6%) |
These figures assume that the two genes are inherited independently. If they were physically linked, the real odds would differ.
How to read the result
Read every percentage as the chance for one egg. A pair of hets has a 25% chance of an Amel (Albino) egg each time, so a clutch of two eggs is not guaranteed to hold one. The chance that a clutch of two contains at least one is about 44%, so small clutches stray far from the ratios.
The ratios describe the long run across many eggs, not a single clutch. Do not sell a hatchling as a proven carrier on a ratio alone. Proof comes from breeding records, such as a normal looking animal that produced an Amel (Albino) offspring.
Keep pedigree notes for each animal: parents, hatch date and every pairing result. The color guide helps match a visible pattern to its hobby name before you enter a parent in the tool.
Sex is set by temperature, not by the pairing
The tool does not predict sex. African fat-tailed geckos use temperature dependent sex determination, which a review of reptile sex determination lists for this species. The Animal Diversity Web reports incubation at 24 to 28 C producing mostly females, 29 to 30.5 C roughly equal numbers, and 31 to 32 C mostly males.
Merck notes that sex in reptiles can be genetic or tied to incubation temperature, depending on the species. In this gecko the temperature effect means the parents supply the trait genes, while the incubator influences the sex ratio. A trait chance and a sex chance are separate questions.
Limits of the fat tail gecko morph calculator
| Limit | What it means for results |
|---|---|
| Hobby labels | Trait names and modes come from breeders and are untested in this species |
| Per egg odds | No clutch is guaranteed to match the ratio |
| Different genes, same look | Two Amel (Albino) lines may not combine as the tool assumes |
| Unclear traits | Names with unknown inheritance are excluded from the tool |
| Sex | Set by incubation temperature, so it is not calculated |
No source opened for this page documents a health problem tied to a specific fat-tailed gecko morph, so this page makes no such claim. If a breeder reports one, ask for the evidence. For a group wide view, the gecko morph calculator covers other gecko groups.
Learn the wider reptile picture from the morph index, and keep husbandry questions for the species guide.
Frequently Asked Questions
Can a fat tail gecko morph calculator tell me if my gecko is a het?
No. It only turns parent genotypes into odds. A het is proven by a breeding result, such as a normal looking gecko producing an Amel (Albino) hatchling.
Does the leopard gecko albino research apply to my African fat-tailed gecko?
Not directly. The study found three different albino genes in leopard geckos, so the African fat-tailed gecko line could involve a different one. It shows that similar looking traits can have different causes.
Why are oreo and zulu not in the tool?
Their inheritance is unclear, and no source tested them. Adding them would produce numbers that look precise but have no basis.
Can I choose the sex of the hatchlings?
Not through the pairing. Incubation temperature influences sex in this species, and the Animal Diversity Web lists mostly males at 31 to 32 C. Temperature extremes also carry their own risks, so ask a reptile veterinarian before changing an incubator setting.
How many eggs give a real sample of the odds?
Dozens, not one clutch. With het by het pairings, a single clutch of two eggs has about a 56% chance of containing no Amel (Albino) hatchling at all.
Is a two trait pairing worth the extra math?
Yes, if you want a specific combination. A double het pairing gives the both traits outcome in only 1 in 16 eggs, so plan for several clutches.
Sources
- Animal Diversity Web (University of Michigan Museum of Zoology): Hemitheconyx caudicinctus. https://animaldiversity.org/accounts/Hemitheconyx_caudicinctus/
- Valenzuela: Temperature dependent sex determination in reptiles, Iowa State University, 2004. https://faculty.sites.iastate.edu/nvalenzu/files/inline-files/valenzuela2004_reptiliantsd_chapt09.pdf
- Genetics (Oxford Academic): Candidate genes underlying hypomelanistic morphs in squamate reptiles, 2026. https://academic.oup.com/genetics/article/232/1/iyaf236/8313584
- Merck Veterinary Manual: Overview of Reptiles. https://www.merckvetmanual.com/exotic-and-laboratory-animals/reptiles/overview-of-reptiles