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Name:________________________ Date:___________ Period:________ HW: Solving Monohybrid Crosses in 5 Steps Directions: Grab your paper and pencil. For each problem, be sure to show the work for each step. Problem #1 – Being a taster of the chemical PTC is dominant over being a non-taster (recessive). A man heterozygous for this trait marries a female who is homozygous recessive for this trait. Use a Punnett square to predict the phenotypic and genotypic ratios of the offspring. Step 1 – Choose a letter to represent the dominant trait and recessive trait. T = Taster & t = Non-taster Step 2 - Write down the genotypes of each parent. Refer to the problem above. Mom tt & Dad Tt Step 3 – Write the genetic cross. tt x Tt Step 4 - Write the possible alleles of mom across the top and dad along the side. Fill in the Punnett square. t t T Tt Tt t tt tt Step 5 : Determine the phenotypic and genotypic ratio of the offspring. Don’t forget to label the ratios. Genotypic Ratio: 0 TT: 2 Tt: 2 tt Phenotypic Ratio: 2 Taster: 2 Non-taster Genotypic %: 0%TT: 50% Tt: 50% tt Phenotypic % 50% Taster: 50% Non-taster Assignment_Science7 Name:________________________ Date:___________ Period:________ Problem #2 - In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for yellow peas. **REMEMBER to show your work for steps #1-5. Step 1: Choose a letter Yellow = Y Green = y Step 2: Write the genotypes for mom & dad Mom = Yy Dad = Yy Step 3: Write the genetic cross Yy x Yy Step 4: Draw a Punnett Square Y y Y YY Yy Yy yy y Step 5: Write the genotype and phenotype ratios Genotypic Ratio 1 YY: 2 Yy: 1 yy Phenotypic Ratio: 3 Yellow: 1 Green 25% YY: 50% Yy: 25% yy 75% Yellow: 25% Green Assignment_Science7