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Harry Potter and Mendelian Genetics
This week's Nature has a letter suggesting that Harry Potter be used to teach genetics.
Wizards or witches can be of any race, and may be the offspring of a wizard and a witch, the offspring of two muggles (’muggle-born’), or of mixed ancestry (’half-blood’).
This suggests that wizarding ability is inherited in a mendelian fashion, with the wizard allele (W) being recessive to the muggle allele (M). According to this hypothesis, all wizards and witches therefore have two copies of the wizard allele (WW). Harry’s friends Ron Weasley and Neville Longbottom and his arch-enemy Draco Malfoy are ‘pure-blood’ wizards: WW with WW ancestors for generations back. Harry’s friend Hermione is a powerful muggle-born witch (WW with WM parents). Their classmate Seamus is a half-blood wizard, the son of a witch and a muggle (WW with one WW and one WM parent). Harry (WW with WW parents) is not considered a pure-blood, as his mother was muggle-born.
In order to try out html tables I was going to do some Punnett squares, but they weren't quite right, and I'm lazy. Do them yourself.
2 comments:
I haven't dealt with Punnett squares since high school biology, but I think the anology actually breaks down in Hermione's case.
Her parents are both Muggles, which would not make witchcraft hereditary.
The analogy works just fine. Hermione's parents each have one copy of the wizard gene (W) and one copy of the muggle gene (M). The two genes form a pair.
Father: MW Mother: MW
Since the muggle gene is dominant and the wizard gene is recessive (that is, not expressed in the organism itself), neither of Hermione's parents is a wizard, even though they each have one copy of the wizard gene.
It's like blue eyes in people -- unless you have TWO copies of the gene for blue eyes (that is, unless BOTH of your eye-color genes are blue), you won't have blue eyes. I have one copy of the blue eye gene and one copy of brown/hazel; my eyes are brown/hazel, because that gene is dominant over the blue-eye gene. (Since my husband's eye color genes are both blue, that means that our future kids have a 50 percent chance of having blue eyes; it all depends on which eye color gene they inherit from me, the blue one or the hazel/brown one.)
Hermione's parents can each pass one of their two genes to their offspring. The possible combinations are:
From father W, from mother M = MW(this produces a muggle who is a carrier of the wizard gene)
From father M, from mother W (also an MW muggle carrying the wizard gene)
From father M, from mother M (this produces an MM muggle who does NOT carry the wizard gene -- all of this person's children will be Muggles no matter what. Even if this person marries a wizard, none of the offspring will have any magical abilities, because they need to inherit a W gene from BOTH parents. Having this type of Muggle for a daughter-in-law would be Lucius Malfoy's worst nightmare.)
From father W, from mother W = WW; this child will be a wizard. This is what Hermione is.
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Also, it seems that there must be another gene governing the *expression* of magic, which would work like the gene for coat deposition of color in Labrador retrievers. (A yellow lab is really a black or chocolate Lab which can't deposit the black or brown pigment in its coat; this is also a recessive gene, which explains why two black or two chocolate Labs can produce yellow puppies, two yellows cannot produce puppies of any color BUT yellow (since each parent has two copies of the non-deposition gene, but none for deposition), and a yellow crossed with a black Lab can have black or yellow puppies. I guess a Squib would be a person who is a wizard (WW) but has two genes for non-expression of magic ("xx") rather than one for expression and one for non-expression ("Xx") or two for expression ("XX").
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