1. How are witches and wizards made?
Harry Potter Genetics
How are witches and wizards made?

2. Some Background Info…
The story of Harry Potter is set in a world like our own.
This world is populated by people with magical powers (wizards and witches) and a majority of people without any powers (muggles).

3. Wizards or witches can be of any race, and may be the offspring of:
a wizard and a witch (pureblood aka purebred)
the offspring of two muggles (muggle-born)
or of mixed ancestry (half-blood aka hybrid).
This suggests that wizarding ability is an inherited trait, with the magic allele (m) being recessive and the nonmagic allele being dominant (M).

4. M=non-magic allele
m=magic allele
All witches and wizards have the alleles mm.
All muggles have the alleles MM or Mm.

5. The Potters
James Potter mm
Lily Potter mm
Both Harry’s parents had magical ability so they must both have been mm. m m
They passed these alleles on to Harry.
Harry Potter mm

6. The Malfoys The Malfoys are a ‘pure blood’ family. Draco Malfoy mm
Lucius Malfoy mm
Narcissa Malfoy mm
All their ancestors are wizards so they must have the alleles mm.
The Malfoys are a ‘pure blood’ family.
Draco Malfoy mm

7. The Weasleys
The Weasleys are pure blood wizards so they all have the alleles mm.

8. And what about Hermione?
Hermione is a powerful witch but both of her
parents are muggles…they must be Mm to
pass on the magic allele…
Mrs. Granger Mm
Mr. Granger Mm
Hermione Granger mm

9. Voldemort
He is a half blood… his mother was a witch and his father a muggle.
Tom Riddle, Sr. Mm
Merope Gaunt mm
Voldemort mm

10. Filch…
Filch is a squib…he has NO powers even though BOTH of his parents are wizards (mm).
How could this happen?

11. Now for some problems….

12. Ron Weasley and Hermione Granger end up married
Ron Weasley and Hermione Granger end up married. What chance is there that their children will be witches and wizards? ?

13. Lets work through the problem…
We start with a four square box… a Punnett square.
We place the genotype (alleles) of the parents on the outside of the box…
Then we combine them together to get the possibilities of the children…
m m m mm mm
There is a 100% chance that Ron and Hermione’s kids will be witches or wizards. mm mm

14. What about Harry Potter and Ginny Weasley
What about Harry Potter and Ginny Weasley? Because they are a witch and wizard, the outcome would
be the same as
it was for Ron
and Hermione. mm mm mm

15. So… let’s imagine that Ginny, instead of marrying Harry, married JUSTIN BIEBER! And let’s say Justin’s genotype is MM. Remember, Ginny’s genotype is mm. M M
What chance is there that Justin and Ginny’s kids will be witches or wizards?
ZERO! m Mm Mm m Mm Mm

16. If Hermione had brothers and sisters what chance is there that they would be witches and wizards?
The genotype for both of Hermione’s parents in Mm. We know this because they produced Hermione who is mm.
Mr. and Mrs. Granger have a:
25% Chance of having a witch or wizard
75% chance of having a muggle
M m M m MM Mm Mm mm