Hermione Granger, in her role in the Ministry of Magic, has decided to settle once and for all the genetics of muggle-borns vs witches and wizards. Using data from her own extended family, along with consulting Hogwarts: A History, she has identified two loci that are involved in this question, M and S. She has identified her genotype as mmSS, whereas her parents (muggles) are both MmSs and Mmss. Harry Potter is also mmSs, whereas Ron is mmSS. She even managed to steal some DNA from Mr. Filch (a squib—or non-magical child of a witch and a wizard) and found his genotype is mmss. Based on this information, what can you conclude about the M and S loci
The Correct Answer and Explanation is:
Based on the genetic information provided by Hermione Granger, we can conclude that the m allele at the M locus is necessary for magical ability, and the S allele at the S locus is also required. Specifically, an individual must have a homozygous recessive mm genotype at the M locus and at least one dominant S allele at the S locus to be magical.
Conclusion:
- Genotype mm with at least one S allele (SS or Ss): Magical (witch or wizard)
- Genotype mm with ss: Non-magical (squib)
- Genotype Mm or MM: Non-magical, even if S is present (muggle)
Explanation:
Hermione is a witch with genotype mmSS, yet her parents are both non-magical. One parent is MmSs and the other is Mmss. From this, we can infer that both parents carried the m allele and passed it to Hermione, allowing her to be mm. They also contributed at least one S allele, making her SS. Despite being non-magical themselves, their heterozygous genotypes allowed for a magical child.
Harry Potter is also magical and has the genotype mmSs. This further supports that being mm with at least one S results in magical ability.
Ron Weasley is mmSS and is also magical. His genotype matches Hermione’s, reinforcing the pattern.
Mr. Filch, a squib, has the genotype mmss. He is mm like Hermione and Ron but lacks the S allele. This indicates that while the m allele is necessary, it is not sufficient alone for magical ability. The presence of at least one S allele is also essential. His lack of magical ability despite having the mm genotype confirms that ss results in a non-magical outcome, even if the M locus is homozygous recessive.
Thus, magical ability requires mm at the M locus and at least one S allele at the S locus, establishing a two-locus model with a recessive requirement at M and a dominant requirement at S.
