Readers’ Questions Answered: Genetics and Diet

After a long hiatus, we bring back our “Readers’ Questions Answered”.  In the past we have had 2-3 people respond to each question.  This time around, the single responses we got were so good that we left it at that.  If you have questions you would like answered, please submit them and we will publish them in the near future!

Chris asks…

Is there any difference between a 1-copy and a 2-copy animal as far as dominant genes go and how they are passed along since there are no super forms? would a 2-copy animal still have the same outcome with offspring 50%?

Lisa Brooks responds:  The answer to your question, in short, is that one copy and two copy forms will have different outcomes. 100% of a two copy animal’s offspring will have the dominant gene while a one copy animal will produce a mix of offspring that have the gene and some that do not have it. However, depending on the gene you are working with it may be very easy or very difficult to tell which offspring have the gene and which do not. Below I discuss two common genes to better explain this point: enigma and hypo.

Before I discuss the examples, I think it may be helpful to review the definition of genetic dominance. A gene is considered dominant when one copy of it overrides the copy of the other gene that is present at the corresponding allele. When there is a difference between the one copy (heterozygous) and two copy (homozygous) animal it would be considered co-dominant. A good example of a gene that is co-dominant is the Mack Snow gene as the homozygous or two copy super snow form is very different than the one copy form. A dominant trait, however, will look exactly the same whether it is present in one or two copies. Because they look exactly the same the only easy ways to know if your animal is one or two copy are:
a) knowing the parents’ genetic makeup (i.e. if one parent did not have the gene and one did then your animal must be one copy) or
b) test breeding your animal to an animal you know does not carry the gene. Now onto the examples.

The enigma gene is dominant. More often than not a clear difference between an animal that has the enigma gene and an animal that does not can be easily seen. Test breeding an enigma will tell you whether it is present at one or both alleles. You’ll get 100% enigmas if it is present at both alleles and a mix of non-enigmas and enigmas if it is only present at one.

Hypo is short for hypo-melanism. It is a dominant gene that reduces number and intensity of black spots on a gecko’s body. Genetically it works the same way as the dominant enigma gene. If one copy is present 50% of the offspring will have the hypo gene and if two copies are present then 100% of offspring will have the hypo gene.

However, unlike enigma it can be difficult to tell hypo offspring apart from their non-hypo siblings. This is due, in part because many breeders focused on line breeding hypo animals for even more reduced spotting than the hypo gene alone caused and created a super hypo form. The super hypo form does not necessarily have two copies of the hypo gene (although it may) but has been selectively bred to further reduce spotting. Because of this, offspring from a hypo to normal breeding may have reduced spotting in part because of the hypo gene and in part because of the line bred reduction of spots. Depending on how the genes of the two animals you are breeding interact, it may be difficult if not impossible to tell which offspring are influenced by the hypo gene and which by the polygenic line-bred reduction of spots. This may create a situation in which a gecko appears to have the hypo trait when it really does not.

In conclusion, dominant genes, by definition, always work the same way. Whether the gene is present in one or two copies cannot be determined by looks alone. Unless only one parent could have contributed a copy of the dominant gene you need to test breed to know if the gene is present in one or two copies. If you cannot easily distinguish between offspring that carry the gene and those that do not it will be difficult to know how many copies of the gene your gecko is carrying.

Jamie asks…

I read you actually suggested the Day Gecko diet that Mr. Repashy created (figs and cherry).  I soon will have my first 2 day gecko’s (grandis) and I am bewildered by the array of opinions and studies.  Jon from daygeckos.com replied that his study showed that most diets are not as good as his custom mix (repashy crested + mango baby food + rep-cal wD3).

Elizabeth Freer swear by the study by Finke 2005 saying T-Rex is the only good one (then) at least for gut loading crickets.
Here’s what I want to do, is this ok:
3x a week feed them Pangea Day Gecko
3x a week crickets that I plan to raise with:

• Repashy Bug Burger (Flukers is cheaper but some say not safe)
• 24 hours before I will gutload with Repashy Superload
• Dust with Repashy calcium plus (rather than use their 2 other products together)

Tony Terradas responds: What frugivorous gecko diet you choose to feed your new day geckos is less important than its diet overall. The T-Rex diet you referred to was the original Repashy Diet (v1). Two other great options are “Pangea Fruit Mix Complete” and “Big Fat Gecko Diet”. I’ve had spotty luck with the current Repashy formula (v3) so when I use Repashy I stick to the Day Gecko Diet which, I believe (but could be wrong), still follows the old v2 formula.

The more important thing to consider when feeding your day geckos is that unlike many New Caledonian geckos (crested, gargoyle, leachianus, etc), these powder diets should not be used to replace their insect diet altogether. Supplementing these diets once a week is ample, but the main diet should be a variety of soft-bodied insects like crickets, locusts (EU) or roaches. As you mentioned, gutloading is important for maximizing nutrition for your geckos. Bug burger and similar products work well if you choose not to use apple/orange/potato/oats.
The final crucial element to a complete diet is proper calcium supplementation. For decades, breeders have argued the impact of using UVB light for phelsuma. If you choose to provide UVB light, make sure your calcium powder of choice does not contain vitamin D3. I have never used UVB with my phelsuma and have maintained healthy, prolific animals for several years. I prefer to use Miner-All indoor formula (with D3).

Lisa Brooks is the owner of Carpe Gecko in Toledo OH. She has owned leopard geckos since 2005 and this will be her second season breeding them. Lisa received her PhD in science education from Texas A&M University in 2009 and has worked as a researcher and evaluator on various projects in science and engineering across the US. She also holds degrees in entomology and animal science.  Aside from owning and breeding various reptiles, Lisa is also engaged in designing science curricula that engage students and teachers in real world science experiences, educating the public about insects and reptiles and a multitude of crafts.

Tony Terradas is the owner of Roc Geckos in Rochester, NY.  He grew up catching and learning about local herpetofauna in southern Florida close to the Everglades.  Tony’s eventual passion for geckos led him to begin breeding crested geckos and eventually several other species.  Tony currently breeds Phelsuma grandis and Phelsuma klemmeri, Coleonyx variegatus and several species of New Caledonian geckos (C. ciliatus, C. sarasinorum, E. agricolae, M. chahoua and R. auriculatus).