The allele for brown eyes is dominant to the allele for blue eyes. Which of the following best explains how two brown-eyed parents could produce a blue eyed child?
A-- One parent must be carrying the recessive allele for blue eyes.
B-- One parent must have had only blue eyed parents.
C-- Mutations after fertilization could alter gene sequences and change alleles.
D-- Each parent must be carrying the recessive allele for blue eyes.