Harry Potter Genetics

Genetics Review

• Chromosomes are found in the nucleus• Each human has 46 chromosomes (23 pairs)

• In each pair, one chromosome comes from the mother and one chromosome comes from the father

Genetics Review• The chromosomes are made of DNA• Genes are small sections of DNA• Each gene controls a trait (eye color, thumb shape,

etc.)

Genetics Vocabulary

• Trait: The way an organism looks or behaves• Alleles: different forms of the same trait• Dominant Trait: The stronger trait/the one that will

be shown if the organism carries both alleles• Recessive Trait: The weaker trait/the one that will

be hidden if the organism carries both alleles• Homozygous: Both alleles are the same• Heterozygous: Both alleles are different• Genotype: The genetic code (the allele pair that the

organism carries)• Phenotype: The physical, observable trait based on

the genotype

Genetics Review• For each trait, a child inherits TWO possibilities• One allele comes from the mother and one allele

comes from the father• So we have two alleles for each trait• The alleles in a pair can be the same (homozygous)• The alleles in a pair can be different (heterozygous)

homozygous homozygous heterozygous

Genetics Review• Alleles can be dominant or recessive• Example: Straight thumb (S) dominant,

curved thumb (s) recessive• Possibilities:

• Homozygous Dominant (SS) – there are only dominant alleles, so the child will have straight thumbs

• Homozygous Recessive (ss) – there are only recessive alleles, so the child will have curved thumbs

• Heterozygous (Ss) – the dominant allele is stronger, so the child will have straight thumbs

SS

ss

Ss

The Harry Potter Universe• Wizards and witches have magical abilities• Muggles do not have magical abilities

The Harry Potter Universe• QUESTION: Is the “magic allele” dominant

or recessive?• Discuss the following information with

your partner and use it to decide if magical ability is dominant or recessive.

• Harry’s parents were both magic• Ron’s parents are both magic – and all of

his brothers and sisters are witches and wizards, too.

• Both of Hermione’s parents are Muggles, but she inherited magical abilities.

The Harry Potter Universe• The Muggle (M) allele is DOMINANT• The Magic (m) allele is RECESSIVE

• Harry’s grandparents were both heterozygous (Mm)• Harry’s mom Lily is Magic• Harry’s aunt Petunia is a Muggle• What combinations are possible to make Lily & Petunia?

The Potter AncestorsHarry’s Grandmother

(Mm)Harry’s Grandfather

(Mm)

Magic(mm)

25% chance of being Magic

Muggle(Mm)

Muggle(MM)

Muggle(mM)

75% chance of being Muggle

The Potter FamilyJames Potter

(mm)Lily Potter

(mm)

Magic(mm)

100% chance of being Magic

Magic(mm)

Magic(mm)

Magic(mm)

The Dursley Family

Aunt Petunia(Mm)

Uncle Vernon(MM)

Muggle(MM)

Muggle(MM)

Muggle(mM)

100% chance of being Muggle

Muggle(mM)

The Weasley Family

Mr. Weasley(mm)

Mrs. Weasley(mm)

Magic(mm)

Magic(mm)

Magic(mm)

Magic(mm)

100% chance of being Magic

The Granger FamilyHermione’s parents are both Muggles…

…but Hermione is magic!

(Some people question how Muggle parents can have a Magic child. What can we predict about the genotype of Hermione’s parents?)

The Granger Family

Mrs. Granger(Mm)

Mr. Granger(Mm)

Muggle(MM)

Muggle(Mm)

Muggle(mM)

Magic(mm)

Hermione had a 25% chance of being Magic

Punnett Squares• Punnett squares are a mathematical way to predict

the possible offspring from any two parents.• They are set up like this:

• One parent’s alleles along the top• One parent’s alleles along the left side

Parent 1

Pare

nt 2

Fill in the parent alleles• Hermione’s dad: Mm• Hermione’s mom: Mm

MM

m

m

Fill in the squares• Pull each allele down or across, filling both squares in its

row/column. You end up with 2 alleles in each square.• The squares represent possible offspring.

M

M

m

m

MM

M

M

m mm

m

Make Predictions• Punnett Squares allow you to make predictions about the

likelihood of traits in offspring.• 4 squares = each square represents 25% (adds up to 100%)• Add them up to get probabilities / make predictions

MM: 1/4 = 25%

Mm: 2/4 = 50%

mm: 1/4 = 25%

Genotype Predictions

Make Predictions• Punnett Squares allow you to make predictions about the

likelihood of traits in offspring.• 4 squares = each square represents 25% (adds up to 100%)• Add them up to get probabilities / make predictions

Muggle: 3/4 = 75%

Magic: 1/4 = 25%

Phenotype Predictions

You Try!• Ginny Weasley, who is Magic (mm) falls in love and

marries a Muggle who is (MM). Draw a Punnett Square to predict their offspring.

• What are the probabilities of each genotype (MM,Mm, mm)?• What are the chances of having a Muggle child? A Magic child?

You Try!• Percy Weasley who is Magic (mm) falls in love and

marries a Muggle who is (Mm). • What are the probabilities of each genotype (MM,Mm, mm)• What are the chances of having a Muggle child? A Magic child?

You Try!• If Hermione and Ron (both Magic) have children, what

are the odds of having Muggle vs. Magic children? Use a Punnett Square to prove your answer.

Exit Ticket• Write your answers on a sheet of binder paper• Harry’s grandparents produced one Muggle child

(Petunia) and one Magic child (Lily)• We know Harry’s grandparents were Muggles. But how

do we know that their genotypes were both (Mm)? Is it possible that one or both could be (MM)?

• Draw 3 Punnett squares to show all possibilities (MM/MM), (Mm/MM), (Mm/Mm).

• Use the Punnett squares to explain why BOTH of Harry’s grandparents HAD to be heterogenous (Mm).