Leopard Gecko Genetics

Have you ever wanted to know how the genetics of Leopard Geckos work to produce all the amazing morphs we know and love today? Here we try and cover how the various genetic traits found in Leopard Geckos work.

The basic thing to understand is how morph “genes” work in Geckos.

Genes are found in chromosomes. A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes.

Chromosomes “live” in pairs. It’s the combination of each pair of genes between a pair of “living together” chromosomes which determines what morph a leopard gecko is.

Each gene “pairing”, between 2 chromosomes, behaves in a particular way – Recessive, Dominant and In-complete Dominant. There’s also a 4th term that gets used in leopard gecko genetics – either “Line Bred” or “Polygenic” – we will cover this further down the page.

Recessive Gene Pairs

Recessive gene pairs are “weak” genes. Recessive genes only cause a gecko to “show” a particular morph trait when both sides of the pair of genes are positive for that recessive trait. If we take the example of “Tremper Albino”, a very well known recessive trait:

We shall use “balls” to represent a gene in a gene pair. There are 4 possible combinations of the pair of genes.

If we use “A” to represent a gene carrying “Tremper Albino” and “N” to represent a gene NOT carrying “Tremper Albino”.

  • NN – Both genes not carrying Tremper Albino
  • AN – One gene (left) carrying Tremper Albino – this would be called a “Het” Tremper Albino
  • NA – One gene (right) carrying Tremper Albino – this would be called a “Het” Tremper Albino
  • AA – Both genes carrying Tremper Albino – this would be a Tremper Albino

Earlier, we mentioned how recessive genes are “weak” genes. They only cause a gecko to show a trait if BOTH genes in the pair are carrying the particular morph trait. So, in the above examples for Tremper Albino, only the example where both genes in the pair are carrying “A” would you see a gecko showing the “Tremper Albino” trait. Both the “het” combinations and the “not at all” combination would not cause the leopard gecko to show the “Tremper Albino” trait.

Dominant Gene Pairs

Dominant gene pairs are “strong” genes. Dominant genes cause a gecko to “show” a particular morph trait when either side or both of the pair of genes are positive for that dominant trait. Using the example of “Enigma”, a very well known dominant trait:

We shall use “balls” to represent a gene in a gene pair. There are 4 possible combinations of the pair of genes.

If we use “E” to represent a gene carrying “Enigma” and “N” to represent a gene NOT carrying “Enigma”.

  • NN – Both genes not carrying Enigma
  • EN – One gene (left) carrying Enigma
  • NE – One gene (right) carrying Enigma
  • EE – Both genes carrying Enigma

In the above examples, only the “Not at all Enigma” combination would result in a gecko that wasn’t showing as an Enigma. The other 3 combinations, carrying either one or two Enigma genes, would cause the gecko to show the Enigma trait.

In the world of Leopard Geckos, the term “het” (carrying only one copy of a gene) is usually only used for Recessive genes, not Dominant. Usually with Dominant genes, the number of copies of the gene is stated, rather than stating “het” for a one-copy type.

Incomplete-Dominant Gene Pairs

Incomplete-Dominant gene pairs are “medium-strong” genes. Incomplete-Dominant genes cause a gecko to “show” a particular morph trait when either side or both of the pair of genes are positive for that incomplete-dominant trait but, unlike a dominant gene trait, if there’s only one copy of the gene present, the effect of the gene isn’t as strong as when 2 copies are present. Using the example of “Mack Snow”, a very well known incomplete-dominant trait:

We shall use “balls” to represent a gene in a gene pair. There are 4 possible combinations of the pair of genes.

If we use “M” to represent a gene carrying “Mack Snow” and “N” to represent a gene NOT carrying “Mack Snow”.

  • NN – Both genes not carrying Mack Snow
  • MN – One gene (left) carrying Mack Snow
  • NM – One gene (right) carrying Mack Snow
  • MM – Both genes carrying Mack Snow

In the above examples, only the “Not at all Mack Snow” combination would result in a gecko that wasn’t showing as a Mack Snow or Super Snow. If the gecko carries one copy of the Mack Snow gene, it will show the Mack Snow trait. However, if it carries TWO copies of the Mack Snow gene, the effect of the genes is much stronger and causes the gecko to show the Super Snow trait.

Polygenic / Line Bred Genetics

Sometimes you will hear the term “Line Bred” or “Polygenic” used when talking about traits in Leopard geckos.

“Tangerine” is a pretty common example of a line-bred trait. As is the “blood red” you see in some Hypo geckos and Lavender. Patterning also goes under the “polygenic” category – stripe, reverse stripe, patternless-stripe, jungle, etc – all are polygenic traits.

“Polygenic” simply means “Multiple genes” / “many genes”. A Polygenic / Line Bred trait is one that occurs because of several genes carrying particular little characteristics which, when combined together, cause a gecko to display a certain trait. The reason for calling them “Line Bred” traits is that certainly quite a few of the traits can be “made stronger” by breeding 2 geckos together that both show some of the trait. For example, if you cross a good Tangerine gecko with another good tangerine gecko, you will quite likely end up with geckos that are even more Tangerine than the parents were. Repeating that again and again was what eventually produced the first blood-red hypos.

How does it work if I want to breed 2 Leopard Geckos?

So, how does all of this work when it comes to breeding 2 Leopard Geckos together? Well, for Line-Bred / Polygenic traits, that’s covered in the Polygenic / Line Bred Genetics section.

For other traits (recessive, dominant, incomplete-dominant):

It’s all about the pairs of genes your two “parents” carry.

Your baby geckos will take one of each pairs of genes from each parent.

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