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## Dihybrid Crosses

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**Dihybrid Crosses****Crossing 2 different traits at the same time**1. Determine dominant and recessive traits**Carefully read the problem!**2. Assign letters for the trait**B = black b = white H = Hairy h = no hair**3. Determine genotype for parents***Parents must have 4 alleles (aka 4 letters) Heterozygous black, hairless male = Bbhh White heterozygous hairy female = bbHh**5. Put parent gamete combinations on box**Bbhh gametes: Bh, Bh, bh, bh bbHh gametes: bH, bh, bH, bh Bh Bh bh bh bH bh bH bh**6. Determine the Genotype and Phenotype Ratio**Genotype: 4 BbHh : 4 bbHh : 4 Bbhh : 4 bbhh Phenotype: 4 Black and Hair : 4 White and Hair : 4 Black and Hairless : 4 White and Hairless**Sample Problem**Genotype Ratio: ___ RRYY : ___ RRYy : ___ RrYY : ___ RRyy : ___ RrYy : ___ rrYY : ___ Rryy : ___ rrYy : ___ rryy Phenotype Ratio : ___ Round and Yellow : ___ Round and Green : ___ Wrinkled and Yellow : ___ Wrinkled and Green**Sample Problem**Genotype Ratio: 1 RRYY : 2 RRYy : 2 RrYY : 1 RRyy : 4 RrYy : 1 rrYY : 2 Rryy : 2 rrYy : 1 rryy Phenotype Ratio : 9 Round and Yellow : 3 Round and Green : 3 Wrinkled and Yellow : 1 Wrinkled and Green**Practice Problem**Determine the genotype of the following bunnies: Heterozygous Black-Hairy:_________ White hairless: ____________**Practice Problem**Determine the gamete combinations BbHh: _______________________________ bbhh: _______________________________**Practice Problem**Complete the punnett square:**Practice Problem**Complete the punnett square: BH Bh bH bh bh bh bh bh**Practice Problem**Complete the punnett square: BH Bh bH bh bh bh bh bh**Practice Problem**Give the genotype ratio: Give the phenotype ratio: 4 BbHh : 4 Bbhh : 4 bbHh : 4 bbhh 4 Black and Hair : 4 Black and Hairless : 4 White and Hair: 4 White and Hairless**Extra tips**When determining the probability of events • If the problem states “and” then multiply the chances for each • Chance of heads and heads = ½ x ½ = ¼ or 25% • If the problem states “or” then add the chances for each • Chance of heads or tails = ½ + ½ = 1 or 100%