Crested Gecko Genetics

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.

Defining Morphs

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.

Temperature, Color, & Structure

There have been anecdotal observations that the brightest red crested geckos have smaller heads and crests. There are examples that don’t fit this generalization, however, so it’s another indication there are no hard and fast rules about crested gecko genetics.

Tyrosinase (which controls melanin and other pigments) can be affected by temperature, as in the different “points” coloration in cats: the extremities take on a dark appearance because they are cooler. There has to be a gene in place, however, so that the lower temps allows the mutated Tyrosinase enzyme to become active. That’s why not all cats have color points. These color points are also present in horses (and likely lots of mammals).

There are noted temperature effects on the color of incubating reptiles, including red eared slider turtles and leopard geckos. Higher temps help develop brighter red coloration in leopard geckos while lower temps produce darker brick red colors. It’s possible that temperature influences crested geckos as well. Lower temps and longer incubation (over 90 days) tends to result in bigger babies with bigger head structure and tail pads, which indicate these continue to grow in the egg. Crested geckos hatched at higher temps tend to have smaller heads and tails. It has been noted that color is the last thing to develop before reptiles hatch, so in theory it is possible to raise temps slightly, after a lower temp incubation period for structure, to influence brighter color reds. We do not recommend incubating over 78 as this can cause hatchling death or deformities!

Since red geckos tend to have poorer structure (smaller head widths & smaller crests), there might be something to the correlation between temperature, color and structure. Genetics, age and weight of the female, and incubation temps could be a powerful combination!

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___d*_
N | NN | Nd*
N | NN | Nd*

50% of offspring get spots.

Codom X Codom (Dal X Dal)
___N___d*_
N | NN | Nd*
d*| Nd*| d*d*

Mostly spotty babies

Normal X Super
___d*__d*_
N | Nd*| Nd*
N | Nd*| Nd*

All spotty.

Codom X Super
___d*__d*_
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*| 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!

Summary

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!

23 thoughts on “Crested Gecko Genetics

  1. I am glad to have something on the genes of crested geckos. There never seem to be any super dalmations for sale, so wondered if they do not breed true. I know Lilly exotics have a breeding group. but only seem to have few dal offspring and these are not very spotty. Also the famous red Chips has never seemed to produce offspring with as many spots, well at least I have not seen any photos of any.
    Did read somewhere that a slow incubation produces crested with bigger heads even if both parents have small heads. Also that some people think more reds are produced with a quicker incubation. So if this is the case most reds have small heads ? . Do not think so, my red female from Northern gecko has the biggest head of all my geckos.
    But maybe there is somethings that happens when incubating eggs. That temperature changes at certain times switch on different genes if they are present.
    I have also noticed that there is not s real green. Most people think of green been made with green and blue, but a olive green can be made with yellow and black.
    My two olive coloured geckos fire up almost jet black and most of there offspring are either chocolate or black fired up.
    I think there are only red, black, yellow, and white genes in crested geckos. The combination of yellow and black with red making most of the browns .
    Just trying to breed some good pinstripes by line breeding . Hope this gives you some food for thought, probably talking a lOAD OF RUBBISH.

    • Super dals do tend to breed true, but the babies don’t necessarily have tons of spots when they hatch out. There aren’t a lot of dedicated superdal breeders, but you can check out Dragontown Reptiles they have some available. I wouldn’t trust just anyone who claims to have a superdal baby, but I would definitely trust Mike. I’ve seen a few Chips offspring from gecko forums that lived up to the line. Some pairings just produce better results! :)

      I would say that wider heads can be influenced by incubation temps but there should be some genetic background to influence it. I have babies from a pairing where neither parent has spectacular head structure yet the babies are coming out fantastic. We’ll see how they develop! All our eggs are incubated at the same temps, so that doesn’t necessarily explain it. Longer incubation can result in bigger hatchlings overall, which may in turn influence crests. It very well could have something to do with the timing of changes in temps during incubation.

      Most people have commented on the poor crest and head structure of most reds, so consider yourself lucky! :) Red and yellow color in many reptiles becomes more vibrant at higher temps, which results in faster hatch rates which also correlates with smaller heads. I think there’s something to it, but genetics does play a role as well.

      I agree, I don’t think there is any blue pigment in crested geckos, as with many gecko species, bearded dragons, etc. Olive is just a combination of yellow and black, although through selective breeding we can probably achieve a gecko that appears to be more green than olive. I doubt we’ll be seeing any blue geckos any time soon. :)

      I think there are enough representatives of pinstripes in crested geckos that line breeding isn’t necessary, but may bring out some hidden traits so I wish you luck with that! Thanks for your comments, always good to chat with fellow gene theorists. ;)

  2. I really enjoyed reading about the genitics. I’ve been working with Cream’s and olives and did to notice that Dal spotting was co-dominate. Nice to see it mapped out in a putnam :D

    Now I’m looking at Olive(m) + Yellow Tiger(f), seeing which base color comes up more, or like you state if they seem to blend (HET trait)

    Also I’d like to see the % of Tri-color’s to come out of my Olive (m) with Tri-color (F) if any are to at all.

    Comments?

    • My results with Olive and Yellow have resulted in 2 yellow, 2 olive and one orange! It’s not enough of a sample size, but moving forward I would recommend breeding for a color with two similar animals instead of trying to create a color. Flame and harlequin pattern I think is more predictable. Pattern appears to be dominant over no pattern, which contradicts the prevailing ideas that the wild form is patternless… My tiger to flame pairing has resulted in about 50-50 split between tiger & flame offspring, with no patternless. I think the progression of pattern from flame to harlequin is itself a building upon similar genes – remember that these “morphs” are not genetic morphs as seen in leopard geckos or ball pythons where you have hets and such. This is more like building a new “breed” of dog – you breed for a set of physical characteristics and you don’t tend to isolate recessive traits.

      If your Olive male has any pattern, it should work ok with your Tricolor female. My best tricolor hatchlings have come from good tricolor parents. But you have to start somewhere. :)

      Good luck!

  3. I was wondering, I’ve seen some photos of blue colored crested geckos. Does anyone now how much they cost or where I can buy one? I didn’t see anything in the above discussion about blue cresties. Anyone with info please email me or call 6178956433 thank you:)

    • Hi Noah! Unfortunately, most pictures of blue crested geckos are a scam – there are no true blue crested geckos. It is suspected that crested geckos don’t have any blue pigment. So it is very unlikely we will ever see blue, green or purple crested geckos, or any Rhacodactylus species. The closest we have are olive, which is really a combination of brown and yellow in the color spectrum, and so-called lavender, which is more of a slate grey. Compare that color with the bright greens and blues of Day Geckos and you can see the difference. Please don’t spend a lot of money on anyone trying to sell a blue crested gecko!

  4. There is a form of leachianus that does have purple blotches but they are not in the same genus as cresteds so that trait would probably not show but I am going to go out on a limb here and wonder out loud if it could come out in Gargoyles?

    I also wonder if the seemingly random mash of genetics with crested geckos applies then to the other “Rhacs” aka sarasinorum’s or PI chahoua’s white collar and Leachianus pink mixes and snowflakes

    • There are a lot of factors that affect our perception of colors. Many people think that their geckos are “green” when they are, in technical terms, shades of olive with no blue pigment. To them, it’s green enough to call them that, which is fine as all color is subjective. I have had a crestie that looked very “plum” colored but I think it was a combination of being fired up and being about to go into shed. So there is still a lot of variation that can look close to purple or green within their genes without going towards pure blue. I think that this is the same thing going on with Leachies and other species of Rhacodactylus like Gargoyles. Even though crested geckos have been proposed to the genus Correlophus, they are still very closely related to Rhacs. I don’t think that they currently have a true blue pigment in their genome but there is always a possibility of it being there, just bred out of favor for some reason over multiple generations. It would be great to have some really blue, purple or green geckos as part of the New Caledonian “giant gecko” species!

  5. if you check you tube there is a giant caledonian all green… similar to the color of green tree python…. the guy has a youtube video trying to sell it>>> I think it was a reptile store… “extreme reptiles” or “extreme exotics” or something like that… it is amazing to see. check it out>> it was obviously not captive bred. which makes it even more amazing..

    • I couldn’t find the video, unfortunately. Any New Caledonian Giant gecko would look great in that kind of coloring. When I tried searching, I just got videos of Giant Day Geckos, which truly are green like a GTP.

  6. I have seen a blue crested gecko…, I haven’t seen it since about a month ago but I’ve seen it twice total. Its happened to my male. He is a light green and fires up to a really dark brown. Sometimes though…when he is fired up…his colors stop going so dark and gives off a blueish color. Its not a real blue but looks like the blue you see in dogs…, where the gray and white fur mix together making it look blue. I’ve only seen it twice in two years with this particular gecko…, and what i’ve experienced doesn’t last more than a day. So a true blue crested gecko I still believe isn’t possible but I have seen them blue.

  7. Hi,

    I am a small UK breeder of crested gecko’s and I have been compiling some of my own research in recent years. The two staple areas I have been monitoring are Dalmatian spotting and Pinstriping. Striving for quality over quantity!

    In my experience dalmatian spotting has been about 50/50 when my superdal male has been crossed with non Dalmatian morphs such as Tigers and buckskins, which closely relates to your thoughts.

    Similarly with my pinstripe group last year especially have produced similar results. With Pinstripe to Pinstripe I produce about 80% Pinstripes and 20 % Buckskins. However! All buckskins had suggestive signs of phantom pinstriping. This is a conection I am keen to explore further this year, with the introduction of a third Pinstripe female. Similarly, all my pinstripes are 99-100% complete, and the pinstriped offspring have all featured above 90% complete striping.

    You may also be interested to know there is another UK breeder who is producing Monochrome crested gecko’s. Grey base colour with white dorsal highlights, not dark brown/ almost black like blondes, but ash grey.

    Thanks for the interesting read!!

    • It’s interesting that you report getting buckskins (assuming you mean a patternless, brown colored gecko) when you pair pinner to pinner. All of ours have been either partial or full, with an occasional phantom. I wonder if it’s easier to see the phantom trait in buckskins because nothing else in their pattern “competes” with seeing the phantom pinning? It’s a fairly new morph, and many geckos that would be considered bicolor probably display some phantom pinning. Conversely, a lot of bicolors are now being called phantom pinstripe for a higher sales price.

      I do know of Kat’s grey geckos, they are phenomenal! Very few breeders are working with them and I think they’re going to be very important to breed new or improved colors into cresties!

  8. I breed crested geckos I think I came up with a new morph but not sure. When thy hatched there spots that are on there tail. There tail is all white with long black lines in any length on it I called it pin tail. But has I said do not know. Help

    • You may have found an uncommon trait, but there are already some in existence. Check out the pictures here from Altitude Exotics: . However, I don’t know if anyone is working hard on enhancing that trait, so you may have a niche market available to you! Good luck with your geckos. :)

  9. Hi, though I myself am not currently breeding crested geckos, I find their genetics fascinating and was planning on experimenting with them. I was thinking of starting with varying incubation temps to see if that triggers different genes, or enhances them. I would really appreciate suggestions if you have any, please email me at Clroxr@gmail.com.

    • Hi Elyse!

      If you wantto play with incubation temps, be sure not to get too hot (over 78) or you risk get stunted, small “premature” hatchlings. Higher temps help develop red coloration in leopard geckos and it’s possible in crested geckos as well. So if you have a red pair, you can raise half the clutches in cooler temps and half at warmer temps to see if it affects color. I have heard that lower temps and longer incubation results in bigger babies with better structure. Since red geckos tend to have poorer structure (smaller heads & crests), there might be something to the correlation between temperature, color and structure.

  10. I Incubate my Cresteds at 83 and every baby that comes out is red, dark red and on a rare case bright orange red. But it mite be my female red but every time!!! Every baby from day one was these colors. never had stunted or small hatching’s.

  11. I am just getting started with crested geckos most of my life I’ve been a snake guy and have had a ton of experience with them ….I’ve sold off my whole collection of snakes and now I am getting into crested geckos and leopard geckos…..I have a pair of dalmation that I will be putting together as soon as my female is up to weight…..I’ve read everything here and it has only made me more interested and more curious to see what happens when I start breeding…..

    • It’s always exciting to see what a new pair produces! There are often lots of surprises, and the babies can exceed the quality of the parents. Dalmatians usually pass on their spots very well, so good luck with your project!

  12. When trying to account for the dalmation % offspring, and it not always working out, consider a second On/Off gene that must also be present to show the spots. It is seen in chinchilla color genetics when creating a spotted animal called ‘Mosaic” the animal must be homozygous for mosaic AND have the on/off gene, which I think is dominant for on.

  13. It seems to me like these are a lot like amazon tree boas where it’s not nearly as cut and dry with the morph ratios in a clutch like it would be with corns or bps? With ATBs you kinda get a random mix of garden phases and coloreds cresties seem to have the same thing going on. The genetic rules are loose and don’t completely apply here.

    • You’re right that they have something different than other reptiles. They have a lot fewer dominant and recessive pairs of traits and have more polymporphic traits. It takes a while to learn what to expect out of your breeding pairs.

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