Andrea Klenotiz admits she was not yet a biology major when she first read the Harry Potter books. So, it was only very recently that she came across J.K. Rowling’s statement that the “wizarding gene” is dominant (meaning much more likely to be passed from parent to child).
Klenotiz also noticed the confusion surrounding Rowling’s statement, as a lot of folks seemed to think that the author had gotten one of the basic foundations of genetics wrong. If the wizarding gene was dominant, how could you explain muggle-borns, wizards born to non-wizard parents? And how to explain squibs, the rare non-magical offspring of wizard parents?
“Magical ability could be explained by a single autosomal dominant gene if it is caused by an expansion of trinucleotide repeats with non-Mendelian ratios of inheritance,” Klenotiz writes.
Klenotiz sent Rowling a six-page scientific paper supporting her claim. Fortunately for us, she also shared it with the Internet:
“The Huntington’s Disease Collaborative Research Group (1993) proved that the disease was caused by CAG (cytosine-adenine-guanine) trinucleotide repeats. The Huntington gene is dominant and autosomal (not linked to sex chromosomes). Normally, a person has 11 to 34 CAG repeats in the gene of interest, which causes the transcription of the normal huntingtin protein. Unfortunately, when an individual has 42 to over 66 CAG repeats, the abnormal huntingtin protein transcribed causes serious symptoms later in life [...]
Trinucleotide repeats are inherently unstable, so DNA replication errors, such as slippage, are more likely to occur [...] With the huntingtin gene, some individuals can have an abnormally high amount of repeats but still be phenotypically normal [...] If 100 repeats are necessary for the gene to be of the magical dominant allele variety, the recessive non-magical, or muggle, allele type might only contain about 50 repeats.
So, within a range, most muggles have about 50 trinucleotide repeats, but like any other trait there will be variation and some muggles might have 90 repeats and still be phenotypically non-magical. Muggle-borns are caused by spontaneous mutations.”
Klenotiz’s entire report is worth the read. She goes on to show how the nature of trinucleotide repeats could also explain the occasional birth of some much more magically gifted witches and wizards as well as squibs. She even drives a nail in the coffin of the assumption that “pureblood” wizarding lines are dramatically superior to witches and wizards more closely related to muggles.
“Despite their different heritages, their mutations make [squibs and muggles] genetically similar. This suggests that [squibs'] limited ability to interact with the magical world (seeing Hogwarts and dementors) might be environmentally influenced, rather than genetic. Cross muggle-wizard adoption studies could provide evidence for this hypothesis…”
Klenotiz also attached a 15-item bibliography, which, by the way, only includes one Harry Potter book.