Co-Dominant/Dominant Genetics 301

05 Aug Co-Dominant/Dominant Genetics 301

At this point we’ll assume that you’ve already read our Intro to Reptile Genetics page & are somewhat familiar with the terms we’ll be using going forward. Most of the genetic terms on this page are “clickable” and will bounce you back to the glossary page if you need to refresh your memory.

General Information


Co-Dominant/Dominant Genes – what are they and what do they do?

Genetic inheritance of co-dominant genes works in essentially the same manner as genetic inheritance in simple recessive genes, except for the fact that heterozygous animals are visibly different than normals. These visible “hets” can be bred together to produce an even more extreme variation of the mutation, often called a “Super.” The “Super” is a dominant form of a co-dominant gene, and can be bred to a normal animal to produce entire clutches of the visible het, or co-dominant form. There is a marked difference between the visible het/co-dominant form and the homozygous super form. When we do not see a visible difference between the het and homozygous forms, the mutation is referred to as dominant as opposed to co-dominant. As with recessive mutations, we can use punnett squares to predict the genetics of offspring from a co-dominant breeding in the same manner as discussed above.  One advantage of a co-dominant gene is that we are able to identify the heterozygous and homozygous gene carriers by their physical appearance;  these animals will be visibly different from the normal (or wild-type) offspring.  From a breeding perspective this is especially useful as there will never be “possible-het” offspring. A great example would be the color/pattern mutation of the Pastel phase ball python. This co-dominant mutation expresses itself as the Pastel being the visible heterozygous form of the Super Pastel. When a Pastel is bred to a normal form the resulting babies in theory are 50% Pastels and 50% normals. When two Pastels are bred together we may expect 25% normals, 50% Pastels and 25% Super Pastels. When a Super Pastel is bred to a normal all of the babies are Pastels. Breeding Super Pastels together results in all Super Pastels.

Examples of Co-Dominant & Dominant Traits in Reptiles


The following is a list of genetic mutations in reptiles that have been bred & proven simple recessive. This list is not all-inclusive, but intended to give an idea of co-dominant & dominant genes in the herp world, as well as some of the popular species in which they are more commonly found. As you can see, co-dominant and dominant mutations do not occur as frequently as recessive mutations.


Ball Pythons Boas Reticulated Pythons
Mojave Hypo/Salmon Tiger
Pastel Jungle Super Tiger
Pinstripe Motley
Platinum
Spider
Super Pastel
Coral Glow
Woma

Punnett Squares for Simple Recessive Genes


Note: While we use Pastel ball pythons as our example here, the following punnett squares apply to any co-dominant/dominant mutations in any species.

Normal X Co-dominant Parents


Here we’ll demonstrate a punnett square to show the resulting offspring from breeding a Normal/wild type ball python (NN) to an Pastel ball python (Np*). In this case, the p* represents the co-dominant Pastel gene.

As we can see from the above square, half of the offspring from breeding a Normal to an Pastel should be normal, wild-type/non-gene carriers (NN), and the other half should theoretically be co-dominant Pastels (Np*).

Co-dominant X Co-dominant Parents


This punnett square shows the offspring from breeding a Pastel (Np*) ball python to a Pastel (Np*) ball python.

From this pairing of Pastel (Np*) to Pastel (Np*), we can see that half of the offspring will be Pastels, 25% will be normal/wild-type (NN), and the remaining 25% will be the dominant Super Pastel (p*p*) form. As with recessive traits, the percentages of offspring from breeding co-dominant animals are theoretical. It’s possible to breed Pastel to Pastel & get all Pastels, all Supers, all normals (albeit unlikely), or more typically, a mix of the three, but not always in 50%-25%-25% ratios. Having that Super pop out is a great thing though, and leads us to our next combination.

Dominant X Normal Parents


As stated in our initial explanation of co-dominant/dominant traits, we can see that a dominant animal – in this case a Super Pastel (p*p*) ball python bred to a normal/wild-type (NN) ball python will yield all co-dominant, or Pastel (Np*) offspring.

Dominant mutations have a lot of “combination value” with regards to other mutations. Since you see results within the F1 generation, it’s much easier to use dominant morphs to combine with other projects – i.e. simple recessive color or pattern phases.

Dominant X Co-dominant Parents


The results of breeding dominant to co-dominant are very straightforward:

Np* = Pastel offspring

p*p* = Super Pastel offspring

Theoretically half of the resulting offspring (out of 4 eggs) should be Pastels & the other half Super Pastels.

Dominant X Dominant Parents


Our last punnett square, demonstrating the results of dominant X dominant breeding, yields the following:

Nothing like seeing four little Super Pastels peeking out of their eggs!

Notes


Working with co-dominant & dominant morph projects can be a lot of fun, as you typically see results within the first generation. Remember that any time normal/wild-type snakes enter the picture, there is the possibility of whiffing, or missing your odds altogether. Fortunately that doesn’t happen terribly often, but definitely more often than most breeders would care for. As of this writing, we’re starting to see more combinations of co-dom/dominant genes and other traits, and the future is certainly bright for all of these genetic possibilities!

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