In Harry Potter and the Methods of Rationality, a significant plot point revolves around Harry's discovery of the genetic nature of magic though some very bad science.
I am curious what canon events from the books can contradict this hypothesis.
His hypothesis is the following:
- There is a single magic gene and everyone has either zero, one, or two copies of it.
- (MM) If a person has zero copies, they are a true Muggle. They cannot cast magic; magic will rarely interact with them and many potions/enchanted objects/etc won't work for them; they cannot bear Wizard/Witch children.
- (WW) If a person has two copies, they are a Wizard/Witch. They can cast magic; they cannot bear true Muggle children.
- (WM) If a person has only one copy, they are Squibs. They cannot cast magic but some potions and enchanted items work for them; they can bear either Wizards or Muggles depending on their mate.
- As a person gets one copy of each gene from their parents:
- Two WW can only bear WW just as MM can only bear MM.
- WW and WM have an even chance to bear a WW or a WM. MM and WM will have an even chance to bear a MM or a WM.
- WM and WM have a 50% of bearing WM, 25% chance to bear MM, and 25% chance to bear a WW.
- Any muggle-born wizards were actually born to two Squibs who didn't know they had a magical ancestor.
- Any wizard-born squibs must actually be the result of infidelity with a Squib or a Muggle.
It seems that the canon material should contain a contradiction (besides a basic statement of the definitions) to this hypothesis but I cannot remember one.