5. Two parents, both with brown eyes, have four children. One child has brown eyes, like his parents, but the other three all have blue eyes. One of the children has been learning about genetics in science class and knows that brown eyes are dominant to blue eyes in humans. The student developed the following model of a Punnett square to predict the genotypes of his parents and his siblings. Based on his model, the student claims that only one of the four children should have blue eyes. Which of the following explanations best describes why the Punnett square does not model the traits in the student’s family? (DOK 3)

Question 3 options:

a. The student is reading the model incorrectly. The squares containing Bb and bb all contain the recessive allele. Three out of 4 children should have blue eyes, so the Punnett square does correctly model the family’s traits.

b. Since only one of the children should have blue eyes, according to the Punnett square, the other two children must have developed a genetic mutation before being born.

c. The student is reading the model incorrectly. The capital letter represents the recessive allele, coding for blue eyes, and the lowercase letter represents the dominant allele, coding for brown eyes. Therefore, three of the quadrants contain either BB or Bb, meaning that 3 out of 4 children should have blue eyes. The Punnett square does correctly model the family’s traits.

d. The student is forgetting that a Punnett square is used to predict the outcomes of a genetic cross. The actual results do not always match up to the predicted outcomes.