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Division 2 MST Genetics Unit 2011-2012 Dihybrid Cross Problems Directions: For each of the problems below, complete the following on a separate sheet of paper: A.) List the genotype of each parent described B.) Use a Punnett square to predict the possible outcomes of a cross between the 2 parents. C.) List the genotypes and the number of that genotype present in the offspring for each cross (can write as a ratio). D.) List the phenotypes and the number of that phenotype present in the offspring for each cross (can write as a ratio). Symbols (for pea plant traits): T: tall t: short Y: yellow seeds y: green seeds R: Round seeds r: wrinkled seeds P: Purple flower p: white flower Problems: 1.) Cross a heterozygous tall and round seed pea plant with another seed plant. TR Tr Parents: TtRr x TtRr TR TTRR TTRr Tr TTRr TTrr Genotypic Ratio: 1:2:1:2:4:2:1:2:1 tR TtRR TtRr tr TtRr Ttrr Phenotypic Ratio: 9:3:3:1 heterozygous tall, round tR TtRR TtRr ttRR ttRr tr TtRr Ttrr ttRr ttrr 2.) Cross a pea plant that is heterozygous for purple flowers and homozygous dominant for yellow seeds with a plant that is heterozygous for purple flowers and homozygous recessive for green seeds. 3.) PY PY pY pY Parents: PpYY x Ppyy Py PPYy PPYy PpYy PpYy Genotypic Ratio: 4:4:4:4 Py PPYy PPYy PpYy PpYy py PpYy PpYy ppYy ppYy Phenotypic Ratio: 12:4 py PpYy PpYy ppYy ppYy 3.) Cross a plant that is heterozygous for round seeds and homozygous recessive for white flowers with a plant that is homozygous recessive for wrinkled seeds and heterozygous for purple flowers. Parents: Rrpp x rrPp Genotypic Ratio: 4:4:4:4 rP rp rP rp Rp RrPp Rrpp RrPp Rrpp Rp RrPp Rrpp RrPp Rrpp rp rrPp rrpp rrPp rrpp rp rrPp rrpp rrPp rrpp Phenotypic Ratio: 4:4:4:4 4.) Cross a plant that is heterozygous tall and homozygous for green seeds with a plant that is short and is also homozygous for green seeds. Parents: Ttyy x ttyy Genotypic Ratio: 8:8 Phenotypic Ratio: 8:8 ty ty ty ty Ty Ttyy Ttyy Ttyy Ttyy Ty Ttyy Ttyy Ttyy Ttyy ty ttyy ttyy ttyy ttyy ty ttyy ttyy ttyy ttyy
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