Dihybrid Crosses

1. Dihybrid Crosses Unit 8 Part 2

2. Two-Factor Cross of a heterozygous round yellow pea RrYy

3. Two-Factor Cross Results Resulting offspring: Genotoypes: Phenotypes: 1/16 RRYY (1) Round, yellow: 9 1/16 rryy (1) Round, green: 3 1/8 RRYy (2) Wrinkled, yellow: 3 1/8 rrYy (2) Wrinkled, green:1 ¼ RrYy (4) 1/8 Rryy (2) 1/8 RrYY (2) 1/8 rrYY (2) * Crossing two heterozygous traits will always result in a 9:3:3:1 Phenotypic ratio

4. Let’s work with 2 genes • B = Beautiful b = ugly • T = Tall t = short Dad’s phenotype is ugly and short, genotype is bbtt. Sperm all have ugly and short alleles, bt. bt bt bt bt BbTt BT Mom’s phenotype is beautiful and tall, genotype is BbTt. Eggs can have B or b alleles. Eggs can have T or t alleles. Eggs can be BT, Bt, bT, or bt. Bbtt Bt bbTt bT bbtt bt Math Tip: use F.O.I.L. First, Outer, Inner, Last

5. Dihybrid Punnett Square • R = Round • r = wrinkled • Y = Yellow • y = green • Phenotypic ratio: • Round and Yellow: ___ • Round and green: ___ • Wrinkled and Yellow: ___ • Wrinkled and Green: ___ • 9:3:3:1 ratio • Genotypic ratio: • LOTS of genotype combinations!!!!!! Look! 9 3 3 1

6. What is the varieties of gametes produced? Dihybrid Practice AB, AB, AB, AB Dad: AABB Dad’s gametes: ___________________________ Mom: aabb Mom’s gametes: ___________________________ AB AB AB AB AaBb AaBb AaBb AaBb ab ab ab ab AaBb AaBb AaBb AaBb AaBb AaBb AaBb AaBb AaBb AaBb AaBb AaBb ab, ab, ab, ab

7. What is the varieties of gametes produced? Dihybrid Practice aB, ab, aB, ab Dad: aaBb Dad’s gametes: ___________________________ Mom: Aabb Mom’s gametes: ___________________________ aB ab aB ab AaBb Aabb AaBb aaBb Ab Ab ab ab AaBb Aabb AaBb aaBb aaBb aabb aaBb aabb aaBb aabb aaBb aabb Ab, Ab, ab, ab

8. Dihybrid Practice Dad: AaBB Dad’s gametes: ___________________________ Mom: AABb Mom’s gametes: ___________________________

9. Dihybrid Practice Dad: AaBb Dad’s gametes: ___________________________ Mom: AaBb Mom’s gametes: ___________________________