Question

A middle school student is studying genetics in their science class. They are using punnett squares to determine the probability that a trait will be passed on from one generation to the next. The student creates a punnett square for eye color using the genotypes of their parents. A big B represents the gene for brown eyes, and a little b represents the gene for blue eyes.

Select the statement(s) that accurately describe the outcomes of the punnett square.


The allele for brown eyes is dominant to the allele for blue eyes.


The student had a 50 percent chance of inheriting brown or blue eyes.


In order to have brown eyes, the student would need to inherit the alleles for brown eyes from both parents.


The student had a 75 percent chance of inheriting blue eyes.


In order to have blue eyes, the student would have to inherit the alleles for blue eyes from both parents.

Answer 1

Correct:
- The allele for brown eyes is dominant to the allele for blue eyes.
- In order to have blue eyes, the student would have to inherit the alleles for blue eyes from both parents.

Explanation: If both parents are heterozygous (Bb × Bb), the Punnett square gives genotypes BB, Bb, Bb, bb — a 3:1 ratio. Any genotype with at least one B (BB or Bb) produces brown eyes because B is dominant, so only bb produces blue eyes. That makes brown 75% and blue 25% in that cross, so the statements claiming 50% or 75% blue (and the claim that two B alleles are required for brown) are incorrect.