Have you ever had a ridiculous conversation about fictitious characters on a topic that isn't even plausible? Well, around Halloween time I found this graphic while looking for cartoons about genetics to share with the class I was teaching. It is based off of a Nature article from 2005 (Vol 436, 776) which I randomly ran across today. In this article they propose the idea of using “analogies of direct interest and relevance”, such as Harry Potter, to teach difficult topics in science, such as genetics, to younger children. While this example allows children to relate the topic to something easier to understand, the oversimplification of genetics by postulating wizardry as being inherited in a Mendelian fashion starts an interesting conversation for people who actually know genetics and are avid Harry Potter fans.
By assuming mendelian inheritance with being a wizard recessive to not, then, all wizards would be the same genetically for wizardry (ww). Whether you were full, half or mud, you would require two copies of the recessive allele to show the trait. It is not possible for it to be a dominant trait because muggle parents could never be able to produce wizard children; at least not without mutation (which sounds more X-Men than Hogwarts). Now, here is where things get complicated: unless there was some sort of incomplete penetrance (as they mention in the paper in regards to Neville) or environmental influence in the level of activation of that gene, this would not account for variations in wizarding ability.
In a rebuttal to that paper the following month (Nature Vol 437, 318, 2005), doctors at the University of Cambridge (might as well be from Hogwarts) posed some of the same concerns as me and my fellow graduate students. Hermione is born of muggle parents but is a wizard herself. By assuming that being a wizard is a recessive trait then both of Hermione’s parent would have to be carriers of the wizard gene, or heterozygous for wizarding, to allow her to get both recessive alleles. With both of her parents being heterozygous, odds are there was a wizard in the family somewhere along the line on both sides. It is possible, however, Hermione didn't know of her families potential wizarding past because it’s been many generations since there was a wizard or they kept their powers a secret.
They were also skeptical about the idea of incomplete penetrance being the culprit for Neville’s reduced wizarding abilities in comparison to his comrades because incomplete penetrance is associated with dominant alleles and this phenotype is determined by having none.
I think wizarding ability is greatly affected by level of intelligence, the environment and other non-wizard factors and is also not determined simply by one gene. I propose that there is some form of epistasis happening where multiple genes are interacting along a pathway to determine the phenotype. Multiple genotypes can then produce the same phenotype and there can be possible variants of said phenotype based on which genotype you receive, accounting for varying levels of wizarding ability.
In the rebuttal they state that “it is not possible, from the evidence presented so far, to conclude that wizarding is a heritable trait.” I, however, think with a little time with the series and creativity, the mode of inheritance can be determined (but ain't nobody got time for that).