Both male and female rats have genotype Bb. Based on the Punnett square, Carol concluded that the phenotypic ratio of the monohybrid cross is 2:1:1. What mistake did Carol make?

Question

Responses
A The ratio should be 2:1The ratio should be 2:1
B The ratio should be 3:1The ratio should be 3:1
C The ratio should be 2:1:1The ratio should be 2:1:1
D The ratio should be 1:1:1:1

Answer 1

To determine the correct phenotypic ratio of a monohybrid cross involving the genotype Bb (where B is dominant and b is recessive), we need to analyze the expected outcomes.

In a monohybrid cross between two Bb individuals, the Punnett square would generate the following combinations of offspring:

• BB (homozygous dominant)
• Bb (heterozygous)
• Bb (heterozygous)
• bb (homozygous recessive)

The resulting genotypes would be:

• 1 BB
• 2 Bb
• 1 bb

The corresponding phenotypes based on the dominance of the alleles would be:

• BB and Bb are both expressed as the dominant phenotype.
• bb is expressed as the recessive phenotype.

Thus, the phenotypic ratio of the offspring would be:

• 3 (dominant phenotype) : 1 (recessive phenotype), which simplifies to 3:1.

Given that Carol concluded the ratio was 2:1:1, she is incorrect.

Therefore, the correct response is: B The ratio should be 3:1.