Leopard Gecko Genetics
by Steve Sykes
Leopard gecko genetics is an extremely fascinating subject and one of the reasons leopard geckos are my favorite species to breed. I first studied basic genetics while a freshman in college. We learned about Gregor Mendel, the “father of genetics”, and his experiments with various traits on pea plants (spherical seeds, wrinkled seeds, various flower colors, etc.). I never thought that I would one day be playing with my own genetics experiment in my reptile rooms!
I understand many people have not studied genetics, so I will start by defining the basic terms. I have tried to simplify this subject as much as possible, and will explain concepts using leopard gecko examples whenever possible.
This refers to the typical leopard gecko coloration of black spots on a variety of base colors. The “normal” phenotype is dominant over all recessive traits (albino, patternless, and blizzard). Therefore, a gecko carrying only one copy of a recessive trait would have at least some degree of black spotting.
Normal morph is a term that is often used to describe wild-type leopard geckos. Wild type leopard geckos are usually heavily spotted on a brownish yellow base color. “Normal” phenotype includes the wild type leopard geckos, but also any other morph that is able to produce black spots, including hypo tangerine, high yellow, lavender, pastel, jungle, etc. To avoid confusion, I will use quotation marks around normal when I am referring to the “normal” (dominant) phenotype, but no quotation marks when referring to the normal (wild-type) morph.
This refers to traits that are not expressed when combined with a dominant trait. In order for a recessive trait to be expressed (outwardly visible) the gecko must be carrying two copies of that trait. Recessive traits in leopard geckos include all three strains of albino (Tremper, Rainwater (Las Vegas), and Bell), patternless, and blizzard.
Selective breeding cannot create recessive traits. These traits are the result of a mutation of certain genes that control a specific part of the development of the animal. Recessive traits are usually discovered randomly, there is nothing you can do to increase your probability of discovering a new recessive trait, you just need to be lucky!
This refers to traits that were created through selective breeding over many generations. Traits that are line bred include hypo-melanistic (hypo), tangerine, and jungle.
In the early stages of the development of these morphs the existed as slight variations from the “normal” phenotype. The tangerine morph is an example of a line bred trait and I will use it in my example of how a line-bred trait is created. The development of this trait began with animals that were observed to have a slight amount of tangerine color in the body. These animals were bred together, and some of the babies were showing more tangerine than their parents. These babies were grown up and bred together, and their offspring showing even more tangerine were selected to breed for the next generation. In this manner the intensity of tangerine was increased with each generation, and this process of selection is continuing today.
These traits are not controlled at a single locus (particular location on the chromosome) and hets cannot be created for line-bred traits. Line-bred traits are controlled by increaser-decreaser alleles, meaning the more intense the traits are in the parents the higher the likelihood of observing these traits in their offspring. For example, if you were to breed the nicest super hypo tangerine in the world (super intense orange-red body color with only a few black spots) with the ugliest wild type normal leopard gecko (heavily spotted with black spots on a brownish yellow base color) you would get babies that were likely somewhere in between in coloration and spotting. Babies could be expected to be brighter tangerine and with less spotting than the normal parent, but more spotting and less intense tangerine coloration than the super hypo tangerine parent. There would likely be a spectrum of orange coloration and spotting between the babies, with not all babies appearing exactly the same.
An example of a line bred trait and increaser-decreaser alleles in humans would be height. If a 6-foot tall person were to have children with a 5-foot tall person you would expect the children to fall somewhere in between the parents in terms of their adult height. However, sometimes the children end up taller than their parents as is the case in my family. My father is 5’11” and mother is 5’4”. I am 5’10”, my sister is 5’5”, but my brother is 6’2”. This sort of situation can occur in hypo tangerine leopard geckos as well, where some babies often end up with less spotting and nicer coloration than either of their parents, and is always a welcome surprise!
We use different terms to describe what genes we see and what genes we don’t see.
Phenotype – the outward appearance; the trait(s) the gecko is showing. Example: a gecko IS an albino, a gecko IS “normal” (black spotted), a gecko IS a blizzard, etc.
Genotype – the genes a gecko is carrying (although these may not be outwardly visible)
The examples below may make help you to understand the difference between genotype and phenotype.
“Het” is a slang term for “heterozygous” (“hetero” means different). Heterozygous animals carry one copy of a specific recessive trait (albino, patternless, blizzard) and one copy of a “normal” trait. We have two copies of each gene (one from each of our parents), and in the case of a heterozygous animal it has inherited one copy of a recessive gene and one copy of a dominant gene.
Example: If you were to breed an albino leopard gecko with a non-albino (“normal”) animal, all babies would be heterozygous for albinism, carrying one copy of the albino gene and one copy of the non-albino (“normal”) gene. Remember that because the “normal” phenotype is dominant over the albino gene, the appearance of the animal is “normal”. The term heterozygous only applies to recessive traits, and is often used improperly, as in the case of line-bred traits (hypo-melanistic (hypo), tangerine, and jungle).
This is the opposite of heterozygous. Homozygous means carrying two copies of the same trait (“homo” means same). A homozygous gecko is carrying two copies of the same trait, one copy inherited from each of its parents. Animals that are homozygous for a specific trait would express it in their phenotype.
Example: A blizzard is homozygous for the blizzard trait, and carrying two copies of the blizzard trait. A patternless albino is homozygous for both albino and patternless, and carrying two copies of the albino trait and two copies of the patternless trait.
LINE BRED MORPHS
Hypo means “hypo melanistic”, or reduction of black coloration (spotting). Tangerine just means orange coloration. Super hypo tangerine just signifies an exceptional hypo tangerine. Unfortunately, the definition of a super hypo tangerine varies between breeders. My classification of a super hypo tangerine is a bright tangerine bodied gecko, with no spots on the body, and a reduction of spotting on the head (if not a “baldy” with a completely spotless head). Carrot tail in its basic meaning refers to any amount of orange-red coloration in the tail, which can be observed on many morphs, including albinos, patternless, and hypo tangerines.
Hypo tangerine and carrot tail are both line-bred traits. Therefore you cannot create tangerine or carrot tail hets because these are not recessive traits. But, a gecko with tangerine or carrot tail in its lineage would be more likely to have tangerine or carrot tail offspring if bred with a hypo tangerine or carrot tail. It would be more appropriate to say an animal carries tangerine or carrot tail genes in its lineage (even though it may not be outwardly visible), instead of calling it a het.
As mentioned previously, hypo tangerine and carrot tail were created through selective breeding over many generations. For example, geckos that were observed to show a small amount of tangerine were bred together, and those offspring showing the most tangerine were selected and bred together, and this was repeated over many generations. This selective process is continuing today. Many breeders (myself included) are picking their best hypo tangerines and carrot tails produced each year, many of which are nicer than their parents, and using those geckos as their breeders for the following year. Selective breeding is a powerful force, and the results can be quite dramatic over multiple generations. It is amazing to think that the super hypo tangerines of today were selectively bred from normal, wild type geckos with brownish yellow body coloration and heavy spotting. Some of the hypo tangerines considered “top of the line” five years ago would be considered “bottom of the line” compared to hypo tangerines of today! Baldy hypo tangerines (without spots on the head) are becoming increasingly common these days as selective breeding decreases the number of spots on the head. I can’t wait to see what hypo tangerines will look like in another five years!
Hypo tangerines typically don’t look like too much when they are first hatched. They develop their tangerine and hypo color as they grow, and carrot tail also becomes evident as they age. For this reason many breeders (myself included) do not sell their hypo tangerines until they are subadult or adult size (25-45 grams). This way both the buyer and seller are able to see the true quality of the animal (or lack thereof!).
I consider the “true” carrot tails to be those from the Ray Hine line (from UK) that often have the majority of the tail to be an solid orange-red. However the body is usually pale yellow, much paler than a hypo tangerine. Many breeders are breeding awesome Ray Hine carrot tails with bright hypo tangerines, in the hopes of creating a bright hypo tangerine with an entirely orange tail. Some of the offspring from this cross inherit the less desirable traits from this cross (paler body coloration than the hypo tangerine and less carrot tail than the carrot tail parent), but others show the desired qualities of both parents. This is something that will get better and better each year with selective breeding.
I have chosen a different course in the quest for a bright orange-bodied gecko with an entirely orange tail. Carrot tail coloration is present in the hypo tangerine line and I am selectively breeding to intensify orange body coloration and the amount of carrot tail. As of 2003 I have produced animals with intense body orange and 40% carrot tail, and I expect my hypo tangerine line to become better as the generations go on.
There are three strains of albino leopard gecko, each named after the last name of the person who first produced the particular strain. Las Vegas albino is another name for the Rainwater strain. All three strains are recessive traits, therefore hets can be created for these traits. All three strains of albino are sensitive to bright lights, and will close their eyes tightly if exposed to bright light. Additionally, many will not feel comfortable eating during the daytime due to their sensitivity to light.
Each of these strains are genetically incompatible, meaning if you were to breed a Tremper albino with a Rainwater or Bell albino all babies would be normal looking (spotted) and heterozygous for both strains of albino. Apparently there are three different ways to create an albino!
Every so often I get an email from someone who purchased an albino leopard but was not told the identity of the particular strain. There are some differences between the three strains, but often it is not possible to wager more than an educated guess. Below I will discuss the differences between the three strains.
Eye color is variable between Tremper albinos, ranging from slightly lighter than a “normal” (non-albino) leopard gecko eye, to bright, bright red in young animals incubated at a high temperature (90 degrees F). I have observed the red eye color of young animals often changes as the animal ages to the normal beige color of the typical Tremper albino.
The patternless trait was the first of the leopard gecko recessive traits to be discovered. Patternless leopards were first marketed as “leucistic”, although blizzards are the true leucistic leopard gecko. Once blizzards were discovered “leucistic” leopards were renamed to patternless, although I still see some people using the antiquated name. The patternless trait is recessive and hets can be created.
Patternless animals are devoid of black spotting. Ironically baby patternless hatch with a pattern of darker blotches on a lighter yellow body coloration. This pattern often fades away as they age, but may be visible in some adults. Body coloration is often quite variable, ranging from bright neon yellow to a dull chocolate brown. Exceptional individuals have orange “carrot-tail” coloration on at least a part of their tail. The dull chocolate brown patternless may be the result of low incubation temperature or genetics. Eye color is the same color as the “normal” leopard gecko.
Patternless albinos are one of the newest leopard gecko morphs, and are the result of combining two recessive traits. Hence, patternless albinos are expressing both the patternless and albino traits (both are outwardly visible). The combination of the albino trait with the patternless removes the dark coloration from the patternless, making a bright neon yellow patternless, with a white or pink tail, rather than a purplish or brownish tail in a normal patternless. Many exceptional patternless albinos have carrot-tail coloration in the tail as well.
The majority of the patternless albinos available today are from the Rainwater strain of albino. It appears the Tremper albino gene does not combine as readily with the patternless gene as the Rainwater gene. The reason for this is unclear, but from conversations with leopard breeders that have attempted this cross it appears only 1 out of a couple hundred of double het (het Tremper albino and het patternless) to double het results in a Tremper patternless albino, although you would expect 1 out of 16 to be a patternless albino. Tremper patternless albinos are becoming more common recently, but are still rarer than Rainwater patternless albinos. The few Tremper patternless albinos I have seen up close don't appear much different than Rainwater patternless albinos.
Young patternless albinos can be differentiated from patternless by having pink heads, rather than dark heads. Since these geckos are expressing the albino gene, eye color is lighter than a normal patternless, and I find this to be the most clear cut way to differentiate a patternless albino from a really nice patternless. The eye color of the gecko in question should be compared to both an albino and a non-albino (“normal” or patternless). Body coloration alone cannot always be used to differentiate patternless from patternless albinos because some nice patternless are as neon yellow as patternless albinos.
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Owners: Steve and Debra Sykes (916) 62-GECKO (624-3256), 10AM-10PM PST