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Leopard Gecko


































Gene Basics

Genetics are different for every animal and so is understanding them. If you want to go into breeding it is

extremely important you know the genetic linage of your animal. You don't want to be crossing genes that can

cause a deformity. Genes can be quite complex to understand. So here’s the basics you need to know about genes to breed

or if you just want to learn a little more.

Genes are found on chromosomes in the blood which holds all our genetic information. The site the specific genes are located are called a locus. In every species the genes will be on the same locus, for every individual of that species (let’s take spot colouring in leopard geckos as an example). Spot colour for a white individual with black spots will be on the same locus as orange individual with yellow spots. However, they have different spot colouring, so although the gene is in the same location on the chromosome, the allele (versions of the gene) are different to bring around different colourings.


When paired to make an individual,  they get one chromosome from the mother and one chromosome from the farther for every pair of chromosomes the animal has. Chromosome number varies in species. The genes they can get from mother and father will vary. Now, genes are either dominant or recessive. This is important because this will depend on if they show or not. Recessive genes are often hidden (in morphs this word is known as het) and do not show in the phenotype (physical appearance). Dominant genes on the other hand will show. In order for recessive genes to show, the gene from both mother and father will have to be recessive.

Here’s a table to show you how genes would work on the phenotype of an animal, our mother and father can both be white individuals with black spots (black spots is dominant) but are carriers (het) for the gene allele that gives yellow spots which is our recessive trait.

The letter B is going to represent spot colouring. Capitals has the dominant allele (black) and non-capitals is the recessive allele (yellow)

This would make both mum and dad genes Bb. So if they produce four individuals this would be the likelihood of the genetic outcome


                                              Genes from mother

              Genes from father             |  B           |            b       

                                           B     |  BB        |           Bb

                                           b     |  bB         |            bb


So let’s explain this now what this means for the phenotype, mother and father have given us for offspring and the colours would be as shown

BB= Black spot, does not carry gene for yellow spot

Bb, bB = Both have black spot dominance gene that over rules the yellow spot gene, so the black spot shows, however, like their parents, they carry the gene for yellow spots.

bb = Has both recessive genes, therefore, the individual will show yellow spots.


Now, the reason this is important (and a very basic model as some genes are paired with other genes and the outcomes get far more complicated) is because many of the traits that are dangerous are recessive and you don’t want to cross them. For example the

trans gene in bearded dragons, if this is crossed there will be deformities, the same with the enigma gene in leopard geckos.

So you need to know how genes work to make sure you don’t cross any animals that are both het with the dangerous gene.

You shouldn’t have any problems crossing that one gene if only one parent holds the gene as there isn’t a chance for another recessive allele of that gene to show, so it will not affect the individual as the dominant gene will take over.

Check their blood lines though, because if it’s been in recent generations but not this individual then stay

away from crossing the two possible gene holders as there can be genetic throw backs.