The mention of the word Genetics, is often enough to make anyone outside of the science community shudder. However for those of you that what to take your reptile passion to the next level and begin breeding you’ll find it very helpful to know some of basic mechanics behind genetics as well as the general terms used within this subject. Our goal with this article is simply to introduce you to some of the basic element and how they apply to reptiles.
Many genetic words are used extensively in reptile lingo and so we thought the best place to start would be with a basic definition of many of these frequently used terms:
General Genetics
- Gene: What causes traits/characteristics to be transferred or inherited to an organism’s offspring.
- Genotype: Describes what an organism’s genetic composition is made up of.
- Heredity: Passing of genetic characteristics from parents to offspring.
- Phenotype: Describes what an organism’s external appearance looks like, which is a result of its underlying genotype.
Gene Terms
- Mutation: An abnormal random gene that can cause an animal to be born with an appearance other than wild-type.
- Dominant: Describes a gene that will produce the same appearance in the offspring – even if it is not paired to the same gene.
- Recessive: Describes a gene that will only produce the same appearance if it is paired against the same gene.
- For example if a reptile inherits a dominate gene for wild markings from one parent and a recessive gene for albino from the other parent – the dominate gene will be displayed in the reptile’s appearance and the albino gene will be masked. For the recessive gene of albino to be displayed by the reptile it must be inherited from both parents.
General Genetics
- Het or Heterozygous: Describes an animal that carries two different genes for a given trait. The animal will display the dominant trait it carries but will also carry the genetics for the recessive gene.
- Possible Het: Term used to describe an animal that has either a 50% or 66% possibility of being “heterozygous” for a gene
- Homozygous: Describes an animal that carries the same gene for a specific trait. A recessive trait must be in its homozygous form for it to display the trait.
- Co-Dominant: A co-dominant animal is heterozygous for the dominant form of its mutated gene, yet is different in appearance than both the wild-type and homozygous forms.
- Super: A co-dominate mutation in its dominant form, essentially the super form of a co-dominant gene.
Some an example of supers would be the Mack Super Snow leopard gecko. Any time that a super is bred to a normal wild type then all of the offspring will show the het homo form of the super. So in leopard geckos all snows will be produced. The super form is a great addition to a breeding group as it opens up a whole new way to create new morphs when crossed with other genetically proven animals.
Appearance Descriptors
- Albino or Ameleanistic: No, or minimal black or brown pigment
- Anerythristic: No red pigment
- Axanthic: No yellow pigment
- Hypomelanistic: Displaying less black and/or brown pigment than a wild-type
- Leucistic: Pure white with dark eyes
- Melanin: Black or brown skin pigments
- Melanistic: Abnormally dark due to an increase in melanin
- Normal: No mutated genes and will display typical natural or wild appearance
- Tyrosinase: Enzyme required for synthesizing melanin
- Tyrosinase-negative or T-: Albino whose cells lack tyrosinase, display a white and yellow/orange appearance with pink eyes.
- Tyrosinase-positive or T+: Albino not able to synthesize melanin, but capable of synthesizing tyrosinase, which results in lavender-brown skin color.
- Xanthic: Displaying increased yellow.
So what does this all mean?
Genetics is all about how traits get passed down from one generation to the next. From the terms above you can see that it is not as simple as just looking at the traits a reptile may display because they also can carry underlying traits/genes that they will pass along to their offspring. A basic knowledge of how dominate and recessive genes work will take you a long way in understanding and developing selective breeding projects.
When two animals reproduce they “send” half of their DNA (genetic makeup) to their offspring. Every animal has two copies of each gene they carry, one inherited from the father and one from the mother. The best genetic tool for helping to understand how genes are passed along is the Punnet square. This square uses the genes each parent carries to calculate the combinations of genes for the offspring.
To illustrate we will use two different examples using the recessive gene of albino and the dominant gene of wild type. Remember for the recessive gene to be displayed, the offspring must inherit a copy of the gene from both parents. However even though a gene may not be displayed it can still be passed along to the offspring.
Example 1
Mother displays albino and carries a double albino gene (A,A). Father displays wild type and carries a double wild type gene (WT,WT).
In the Punnet squares below, albino will be displayed by “A” and wild type by “WT”.
The results of this pairing will result in all offspring displaying the wild type characteristics but will also carry or be het (heterozygous) for the albino gene.
Example 2
For this example let’s take two of the offspring from above and breed them together. Both parents display wild type but are het for albino so they each carry one wild type gene and one albino gene (WT,A).
The results here are:
- 25% display wild type (homozygous wild type)
- 50% display wild type and are het albino
- 25% display albino (homozygous albino)
Here’s where it gets even more interesting, given there is no cost effective way of identifying which animals are in fact het for albino and which ones are homozygous wild type, the normal looking offspring will be called 66% het for albino. Purchasing an animal from this group would give you a 66% chance of having an animal that carries the albino gene, which is called het albino.
The Punnet square is an excellent tool for understanding the potential combinations and theoretical percentages of a breeding pair. However, we can’t forget the role of Mother Nature, some times the percentages work out close to what science tells us and other times they can be very different. One way to think of it would be to imagine a bucket filled with 50 red marbles and 50 blue marbles. If you only took 4 marbles out you could end up with 4 red or 4 blue. It’s the same with genetics, if you produce a smaller amount of babies you could end up with “all the same color” meaning that you could get lucky and get all the visual morphs or you could get none.
Selective breeding projects have become increasingly more complex with reptile breeders combining multiple genetic traits. By doing this the Punnet square increases both in size and in the potential possibilities. These breeding programs can often take many years for the visual genetic traits to be visually produced. Patience and meticulous record keeping is required but the results are one of the most exciting and dynamic aspects of breeding reptiles today. Waiting to see what combination of genetics is going to be displayed in each new hatchling is simply an amazing experience.