Complete question:
A female is born with attached earlobes, which is a recessive phenotype. Which of the following statements about her parents must be true?
a. neither has the codominant allele.
b. Her father has an inactivated allele.
c. Both parents have the recessive allele.
d. Her mother carries the dominant allele.
Answer:
c. Both parents have the recessive allele.
Explanation:
A recessive trait is expressed in homozygous recessive genotypes only. If a female expresses the attached earlobe phenotype, she should be homozygous for the allele since the attached earlobe is a recessive trait. If allele "a" gives attached earlobe phenotype in homozygous genotype, the genotype of the female would be "aa". This means that the female has got one copy of the allele "a" from her either parents. Therefore, both her parents should have at least one copy of the recessive allele "a".
