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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?
The ratio is 9:3:3:1 because there are four unique types of gametes, and the total number of squares is 16. The numbers add up to 16.
The ratio is 9:3:3:1 because you count the total number of dominant alleles (R and Y) in the Punnett square, which happens to be 9, and the total number of recessive alleles (r and y), which happens to be 7.
The ratio is 9:3:3:1 because you must count the number of squares containing at least one dominant allele for each trait to represent the dominant phenotypes and then count the squares with homozygous recessive genotypes for the other phenotypes.Â
The ratio is 9:3:3:1 because 9 squares are showing the dominant phenotype for both traits (Round/Yellow), 3 squares showing dominant for shape and recessive for color (Round/green), 3 squares showing recessive for shape and dominant for color (wrinkled/Yellow), and 1 square showing recessive for both traits (wrinkled/green).
​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?
3/16
1/16
1/4
9/16
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?