We’ve heard a couple of phrases used to describe crested gecko breeding: a crap shoot; a box of chocolates; random.
Crested gecko genetics have been called unpredictable since these geckos became a popular, even mainstream, pet. There is not a lot of readily available documentation on breeding for specific morphs (ex: harlequin) or traits (ex: pinstripe). Baby crested geckos can hatch out as carbon copies of their parents or completely different from them. Some are “nicer” in color and structure, others may look quite plain compared to their progenitors. Often you see a mixture of the two parents.
Why is this?
Crested geckos are considered polymorphic. In fact, the word “morph” comes from the term “polymorphism” which refers to the presence of multiple, visually distinct forms of a single species. See our morph guide for more information on these different phenotypes and basic genetics; this section is to discuss the building blocks for creating morphs and how these genes are passed on during breeding.
Mutations vs Selectively Bred Traits
Many people like to call crested gecko genetics “random” because the morphs do not behave in the numerically predictable manner of reptiles such as leopard geckos, boas, pythons, etc. Those species are able to be categorized into morphs based on their recessive genetic mutations: albino, blizzard, striped, carrot tail, etc. These are based on one gene (or a combination of genes in the case of double or multiple recessive morphs) being able to be passed down in Mendelian fashion. A recessive gene for an albino mutation is often hidden within the gene pool within normal looking carriers called “hets” (from heterozygous). When hets breed, 25% of the offspring are albino based on Mendelian genetic statistics. The recessive morphs cannot be created, they must be present in the gene pool to surface through breeding.
Selectively bred traits can be improved upon through many generations of captive breeding. These are often termed “line bred” traits as inbreeding is usually used to concentrate and fixed within the line. In crested geckos, colors have been selectively bred to be more vibrant and deep. Dark brown near black, high red, clear yellows and bright orange are all favored and bred over muddied colors. While these colors have genetic controls, they are not strictly defined by a Dominant/recessive relationship between the alleles, as in the allelomorphic reptiles (leopard geckos, ball pythons, etc). There are alleles that increase or decrease pigment (or other traits) that produce variation within offspring. In this way, it is possible and expected for offspring to display a range of variation, especially when parents do not share the same alleles. By selecting animals from one end of the spectrum or the other you have a good starting point for creating your own line for a specific trait.
Note that there may be different genes for similar colors, or other contributing factors, so theoretically, non-red babies could result from red to red pairings.
I believe it will just take some time and effort, as well as breeder collaboration, before we can break down the broad phenotype categories into specific genotypes.
Phenotype vs Genotype
Because other reptiles have been mapped out, their genotypes are known and described according to their phenotype. An albino offspring will always (statistically speaking) eventually be produced when you breed two “hets” together, and albino pairings will always produce only albinos. Once we know an animal’s genotype, we can then accurately predict the phenotypes produced.
There are no hets so far in Crested Geckos and no statistical guarantee to get a certain morph when bred to another morph. These morphs are very broadly defined compared to other reptiles. We have categories of what things look like (phenotype) that probably don’t correspond to the genes behind it, unlike with the others that breed true with dominant/recessive, incomplete dominant, or co-dom genes. It’s more like dog breeding, building on what you like and weeding out what you don’t. Even horse breeding has solid genetic science behind it and some genes can be predictable with punnet squares.
Individual traits are transfered to offspring more reliably than morphs, which I tend to think of as the general patterns (patternless, tiger, harlequin, etc). Some amount of pinstripe, dalmatian spots, fringe and knee caps are traits that are readily passed down from each generation. A couple of generations ago, there were few geckos that displayed these traits, and now many have the genetic predisposition for them.
Since our crested gecko morhps are generally just descriptions on patterning that usually preclude any others. It starts with patternless/bicolor, then tiger where the pattern is restricted to vertical stripes on the body. When there is a different type of dorsal than the body, this results in the flame morph which describes a patterned dorsal and the presence of some patterning on the sides/belly. The harlequin morph is a flame by default, with random patches of other colors over the body, including the limbs. There may or may not be a restriction gene that keeps the color markings off of the limbs, it could simply be that harlequins are further along the spectrum of body markings than the flame, as some are also called “low quality” or “borderline” harlequins.
This gets pushed into “extreme” territory when the amount of secondary colors on a harlequin outweigh the base color. This is where the patterning kind of looks like tiger, but the distinction is in which is the base color and which are the marking colors. Generally, tigers are lighter than their marking colors (tiger stripes). In some cases, the tiger stripes are red instead of black. We’ll talk about color in another section.
Because the genetics on the patterning is probably not firm, there are intergrades and variants – the “unique” category. Most patternless and bicolors have some faint markings that could be considered weak tiger markings. Tigers could be the stepping stone between patternless and harlequin but IMO I think there is a distinct gene for the differences in patterning that precludes a tiger from also being a harlequin.
The presence of markings seems to be dominant; I theorize this because there are relatively few patternless geckos. However, this could be due to captive breeding preference towards tigers and harlequins which are higher up on the “patterning” spectrum.
Crested Gecko Lineage
A crested gecko’s background may be a key indicator as to what it will throw during breeding. In one person’s experience, a patternless paired to a tiger may only reproduce tigers. That same tiger, when paired with a flame may produce predominantly flames. In my limited experience, pairing a female flame to a male tiger produces close to 50/50 flames and tigers. A lot of this could be due to the genetic spectrum above but also the lineage (the family tree) of the gecko in question. My yellow tiger to yellow tiger pairing, from a long line of tigers, has predictably produced only tigers. This is the same male tiger who produced 50% flames when paired with a flame.
Crested Gecko Color Genetics
I’m pretty sure color works in the same manner as other animals, we just have to find out the corresponding genes. Guppies, for example, have at least 8 different genes to produce/display a black color. It’s gonna take a long time if cresties are the same way.
I’m currently exploring horse color genetics (another species that is polygenic and had a mystique around genotypes) and find the existence of the “red factor” or Extension gene really interesting. In horses, the coat is either red or black. All existing coat colors are a result of dilution genes on a red or black base color.
ee= Homozygous Red
EE= Homozygous Black (or “NoRed”)
The offspring of a Homozygous Black would never be red. A heterozygous animal may appear to be black or dark brown and be able to produce red offspring. In horses, light reds bred together can produce dark chestnuts but dark chestnuts only produce dark chestnuts – this seems to be the results of pairing dark browns/blacks to reds: a dark “chestnut” red.
Now to get even more off-the-wall, let’s think about incomplete dominance or co-dominance as it is often referred, when breeding crested geckos.
There is a slight difference in the two, but the reptile community tends to lump both together under the label of co-dom. Why? It’s easier. Both states result in hets that look like an in-between phenotype, the difference is with whether the state requires a “non-functioning” gene, which results in an “incomplete” function of the genes when paired. With co-dominance, both states are freely expressed with no competition between the two. The phenotypic look is developed from the merging of these genes’ expressions. This is an important distinction if you want to understand what is going on “under the hood” with your breeding pairs.
With both states, we have an intermediate appearance between two homozygous parents. To pull a page out of horticulture, let’s look at red and white flowers and their offspring. Put simply, take Red (RR) and white (WW) = 100% RW Pink offspring. There is no “pink” gene, it is just the het state. Does this apply to lavender color as an “in between” red and black in crested geckos? Many people have reported good success when breeding the lighter lavender color with reds to produce more reds. Using a darker, chocolate color in a red breeding group tends to result in less true reds and more earthy tones.
This assumes a simplicity that’s probably not the reality. We don’t get 100% anything in crestie breeding. Probably because things are in heterozygous vs homozygous state. But if we can get to a homozygous state through experimentation and good record keeping, we can probably muddle through crestie genetics over time.
The use of horses as models for crested gecko genetics may also be apt to describe the distribution of pattern along the body. White spotting is characteristic of many breeds. In addition, no known albinos exist in horse genetics – which fits right in with what we know of crested geckos. Of course, this may change as more research is conducted! I expect to be proven wrong.
More on crested gecko color genetics coming soon!
Dalmatian Spot Genetics
There is a good deal of evidence that dalmatian spots are a co-dominant genotype.
In the more familiar dominant inheritance, there is no visible difference between the het and homozygous dominant forms. Offspring can be pure wild-type OR hets, you can’t tell which – they are all “possible hets”.
In co-dominate inheritance, there are visible “hets” which produce an even more extreme variation of the gene – a “Super” – when bred together. This co-dom dominant (dominant homozygous) form can be bred to a normal to produce the visible het (co-dom).
Co-doms never have “possible-het” offspring.
Dalmatian X Dalmatian = Super Dal
Dalmatian X Normal = 50% normal*, 50% Dal
* Normal may still have a few stray spots, no set # of spots for deciding a dalmatian.
Let’s Punnett square this biyatch:
Normal (or non-dalmatian in this case) = NN
Codom (or Dalmatian) = Nd*
Super (Super Dal) = d*d*
Normal X Codom (Dalmatian)
N | NN | Nd*
N | NN | Nd*
50% of offspring get spots.
Codom X Codom (Dal X Dal)
N | NN | Nd*
d*| Nd*| d*d*
All spotty babies
Normal X Super
N | Nd*| Nd*
N | Nd*| Nd*
Codom X Super
N | Nd* | Nd*
d*| d*d*| d*d*
50% dals, 50% super dals
Super X Super
d* | d*d*| d*d*
d* | d*d*| d*d*
All super dals!
The problem with this theory is that it doesn’t match everyone’s experience. Another crested gecko dalmatian theory has been laid out in the Pangea Forums that gives a numerical expression of what to expect, resulting in the offspring gaining half again more spots than the average number of spots of the parents.
I do not currently work with Dalmatians therefore I don’t have any personal experience to add!
My current theory is that most cresties are either a mixture of numerous heterozygous states or there are few to no simple recessive genes. Because most “morphs” do not breed 100% true yet are more likely to produce their patterning, this leads me to believe “morphs” are combinations of co-dom genes and selectively bred traits.
In order to say definitively that traits are not recessive, dominant or co-dom, you need to undertake a large number of breeding trials with individuals’ lineages are known. Unfortunately, this is outside my realm of possibility, so I think it’s best to share our experiences with others and hopefully work together to come up with a unified theory of crested gecko genetics!