Unattached earlobes (EE or Ee) are dominant over attached earlobes (ee). A couple has unattached earlobes. Both notice that one of their parents on both sides have attached earlobes (ee). Therefore, they correctly assume that they are carriers for attached earlobes (Ee). If the couple proceeds to have four children, then
A) they can be certain that three will be heterozygous and one homozygous recessive.
B) if the first three are heterozygous, the fourth must be homozygous recessive.
C) the children must repeat the grandparents' genotype (Ee).
D) all children must have unattached earlobes since both parents possess the dominant gene for it.
E) two heterozygous, one homozygous dominant, and one homozygous recessive is a likely outcome, but all genotype ratios are possible.

Question

Quizplus · Accepted Answer

Since both parents are carriers (Ee) for attached earlobes, there is a 25% chance that each child will inherit the recessive allele (ee) and have attached earlobes, and a 75% chance that they will inherit at least one dominant allele (E or e) and have unattached earlobes. The possible genotypes for the children are therefore: EE (25%), Ee (50%), and ee (25%). This translates to two heterozygous (Ee), one homozygous dominant (EE), and one homozygous recessive (ee) as likely outcomes, but all genotype ratios are technically possible.

Unattached Earlobes (EE or Ee) Are Dominant Over Attached Earlobes