Genetic Testing
Genetic Testing
[Cueball and Megan are talking to each other.] Cueball: I sent a DNA sample to one of those "Trace your ancestry" projects. Megan: How legit are those? Cueball: No idea. I just figured it'd be fun.
Six weeks later... [Cueball walks towards Megan with a letter in his hand.] Cueball: Sweet, got my results back. Megan: Ooh, share!
Ancestry Report 48% Labrador Retriever 35% Beagle 12% Cocker Spaniel 5% Other
[Megan is holding the report.] Megan: I think you sent your sample to the wrong service. Cueball: Just in case, I should probably start avoiding chocolate.

Cueball has sent a DNA sample to a genetic genealogy company. The implied premise of the comic is that Cueball intended to send his own DNA to one of the several companies that analyze human DNA samples and provide a report as to the genetic history of that person - examples include notable/famous ancestors or relatives, ethnic background, risk factors for certain medical conditions, etc. However, the result that Cueball receives is consistent with a report for a dog pedigree test, breaking down the percentage of certain breeds present in a dog's ancestry. Megan suggests that Cueball has sent his sample to the wrong company. Cueball appears to agree in principle, but (seriously or jokingly - it is unclear) indicates that he intends to hedge his bets and avoid chocolate just in case he actually is, in fact, a dog. Dogs are generally susceptible to poisoning from theobromine , a compound found in chocolates which causes seizures and heart failure in dogs (and many other creatures). Basically, if Cueball really is a dog, then eating chocolate could kill him.
82% or 94% of genes (depending on how you measure it) are shared between humans and dogs. National Geographic erroneously reported that only 5% of human DNA is shared with dogs and mice, which may have misled Randall Munroe. This leads to several possible interpretations of the comic: It is possible (as Cueball suggests in the last panel) that he is, in fact, a dog with excellent human impersonation skills, or that he somehow shares DNA with a dog. It is possible that Cueball mistakenly sent a sample of a dog's DNA (perhaps his own) somehow thinking that is the method of testing his own DNA. Perhaps Cueball submitted his own (human) DNA to a dog pedigree company and their method of testing includes a presumption of dog DNA, and therefore was able to produce this result from Cueball's sample. Or perhaps this comic is a suggestion that some DNA test companies are scams that do not even perform DNA tests, but simply send out arbitrary reports that are not based on any testing.
The title text refers to the fact that certain dog breeds are more or less susceptible to disease. The diseases he mentions, elbow dysplasia , heartworm , parvo virus and mange are several diseases that can end up killing, disfiguring or disabling dogs, but which humans are generally not susceptible to. As noted above, ancestry DNA test results can inform people about their genetic risk factors for disease, either by specifically investigating your own DNA for those risk factors or, more likely (and less costly) by informing of what risk factors are generally prevalent in your ancestry or others people sharing the same ancestry as you.
After this comic was published, it was revealed that a testing service issued reports determining that First Nations ancestry was detected in sample DNA taken from a dog.
[Cueball and Megan are talking to each other.] Cueball: I sent a DNA sample to one of those "Trace your ancestry" projects. Megan: How legit are those? Cueball: No idea. I just figured it'd be fun.
Six weeks later... [Cueball walks towards Megan with a letter in his hand.] Cueball: Sweet, got my results back. Megan: Ooh, share!
Ancestry Report 48% Labrador Retriever 35% Beagle 12% Cocker Spaniel 5% Other
[Megan is holding the report.] Megan: I think you sent your sample to the wrong service. Cueball: Just in case, I should probably start avoiding chocolate.
