Dihybrid Cross A cross between individuals which examines

Dihybrid Cross A cross between individuals which examines and predicts TWO trait combinations at one time Example: Let’s examine a dog’s hair color AND a dog’s eye color Brown hair (B) is dominant to white hair (b) Green eyes (G) are dominant to blue eyes (g)

Remember… • Law of Segregation: – Alleles for the same gene separate during meiosis. – B’s will separate from B’s – G’s will separate from G’s • Law of Independent Assortment: – Allele pairs (traits) separate independently of other allele pairs (traits). – Hair color and eye color in dogs do not depend on one another

Mommy Dog • Let’s say our mom dog is heterozygous for her brown fur and heterozygous for green eyes. • What is her genotype? • Bb. Gg • She can produce eggs with what combinations? Remember, the B alleles and G alleles will get split during meiosis!

Bb. Gg FOIL! BG Bg b. G bg

Daddy dog • What if the dad is homozygous for brown hair and has blue eyes? • Genotype? – BBgg • Allele combinations?

BBgg FOIL! Bg Bg

Now let’s set up our cross! BG Bg Bg Bg b. G bg

Now let’s set up our cross! BG Bg BBGg b. G bg BBgg Bb. Gg Bbgg BBGg BBgg Bb. Gg Bbgg Bg Bg

By the Numbers • How many offspring have: • Brown fur and green eyes? – 8, 50% • Brown fur and blue eyes? – 8, 50% • White fur and green eyes? – 0, 0% • White fur and blue eyes? – 0, 0%

What about this cross? Bb. Gg x Bb. Gg

What about this cross? Bb. Gg x Bb. Gg BG BG Bg b. G bg

What about this cross? Bb. Gg x Bb. Gg BG Bg BBGG b. G bg BBGg Bb. GG Bb. Gg BBgg Bb. Gg Bbgg b. G Bb. Gg bb. GG bb. Gg bg Bb. Gg Bbgg bb. Gg bbgg BG Bg

By the Numbers • How many offspring have: • Brown fur and green eyes? – 9 • Brown fur and blue eyes? – 3 • White fur and green eyes? – 3 • White fur and blue eyes? – 1

Now try one on your own… • Mommy dog has white fur and is heterozygous for green eyes. • Daddy dog is heterozygous for his brown fur and has blue eyes. • How many dogs would you expect to have brown hair and green eyes? • Brown hair and blue eyes? • White hair and green eyes? • White hair and blue eyes?

bb. Gg x Bbgg

bb. Gg x Bbgg b. G Bg Bg bg b. G bg

bb. Gg x Bbgg b. G bg Bb. Gg b. G bg Bbgg Bb. Gg Bbgg bg bb. Gg bbgg Bg Bg

By the Numbers • How many offspring have: • Brown fur and green eyes? – 4 • Brown fur and blue eyes? – 4 • White fur and green eyes? – 4 • White fur and blue eyes? – 4