
Grade 8 PISA TEST
Quiz by Patrick Brylle Candelaria
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DIHYBRID
A dihybrid cross between two genes in pea plants, seed shape (round is dominant, 'R'; wrinkled is recessive, 'r') and seed color (yellow is dominant, 'Y'; green is recessive, 'y’) is being studied by a genetics student. Two plants that are heterozygous for both traits (RrYy x RrYy) are crossed by the student. The completed Punnett square for this cross is shown below.
Based on the Punnett square, which of the following is the most accurate explanation for how we know the expected phenotypic ratio is 9:3:3:1?

DIHYBRID
A dihybrid cross between two genes in pea plants, seed shape (round is dominant, 'R'; wrinkled is recessive, 'r') and seed color (yellow is dominant, 'Y'; green is recessive, 'y’) is being studied by a genetics student. Two plants that are heterozygous for both traits (RrYy x RrYy) are crossed by the student. The completed Punnett square for this cross is shown below.
Based on the Punnett square for this cross, what is the expected genotypic ratio for offspring that are homozygous recessive for both traits?
