Decoding Desert Ghost by Dr. Benson Morrill of Rare Genetics Inc
As many of you know, we have been working on mapping and designing a test for Desert Ghost for several months now. Well, we now know why it has been so difficult to crack the code on Desert Ghost. Today we will give you a summary of what we have learned about how the Desert Ghost trait is coded in the DNA, and how DG is different from any other ball python morphs that we have studied and designed tests for so far! And last, but not least, we will explain how knowing in depth about how the DG trait is coded for in the DNA will allow us as breeders to be better able to plan our holdbacks and pairings in order to produce a higher percentage of DGs from now on!
First of all, because we are all just learning how DG is different from any of the other ball python morphs we have studied so far, please understand that thinking of DG as a simple recessive single gene morph has worked very well for us for many years now, and now that we know more in depth how DG works genetically, we know why this has been a very good approximation of what is going on with DG. So, for a while it is completely understandable to still refer to DG project animals as simple hets, possible hets, and visuals. But, over time as more people come to understand how the DG morph is actually coded for in the DNA, how we talk about DG project animals will likely change, especially as breeders learn how understanding the coding behind visual DGs can help them produce a higher percentage of visual DG offspring. OK, now we will get down to business! What we have been able to learn about DG is that it is a polygenic trait in which the majority of the visual expression of DG is coded by two different genes that are found on two different chromosomes. We also have evidence that there is at least a third gene that also affects whether or not you get a visual DG…and there could be more genes on top of the three that we have evidence for right now.
BUT, that being said, because this polygenic trait is mostly explained by the genotype of just two genes, it makes it so that as far as polygenic traits go, it is much more like a simple single gene recessive trait than many other known polygenic traits, like height in humans. Researchers recently published a report on genes that affect height in humans and they found that 12,000 genetic variants affect height in humans. So that is a very complex polygenic trait! Thankfully for us, DG is much simpler as far as polygenic traits go. Alright, so how does DG work? Well, we ran sheds from about 300 ball pythons with genetic history known by breeders. Breeders categorized these 300 animals as:
- Visual DG
- HET for DG
- Negative for DG (no DG in either parent to this individual)
What we learned when we ran these 300 samples was that in order for a breeder to call an animal a visual DG, the animal must have at least one mutation in two different genes that
happen to be on two different chromosomes. We are calling these mutations DGa and DGb. Therefore, all four of the genotypes below can lead to a visual DG. VISUAL DG GENOTYPES
- DGa: HET DGb: HET
- DGa: HET DGb: HOM
- DGa: HOM DGb: HET
- DGa: HOM DGb: HOM
So, as you can see here, from the data we have so far, in order to get a visual DG you do not have to be homozygous at DGa or DGb, but you do have to have at least one mutation at both locations.
Therefore, later this year when DG babies have hatched out and you are choosing between buying a nice visual DG combo male and you have the choice between one that has a genotype of DGa: HET, DGb:HET or one that has DGa: HOM, DGb: HOM, the choice would be simple! You would of course want the HOM HOM animal because he will pass on more copies of the DGa and DGb mutations to his future offspring, and therefore a higher percentage of visual DGs will be made from him than from the HET HET male! And for those of you interested, we will certainly go more in depth about possible pairings and % of visual DG offspring in later episodes!
OK, so we know that this is a lot to take in…and now you can all see why this morph has taken us so long to figure out! Getting the locations for these two mutations on different chromosomes has taken quite a bit of time and effort because it made the searching process much more complicated than we had assumed.
But, now we finally have some understanding! And we will continue to learn more about this beautiful DG trait as we run more samples. As we learn more over time, you all fellow Reptile Genetics Nerds will be the first to hear about it on here!
