Biology 1
Monohybrid Cross Practice Problems
Directions: Solve the following genetics problems using the format provided on the Punnett
Square diagrams.
1. In humans, the presence of facial dimples is dominant to the lack of facial dimples. Predict the
possible offspring of a couple where the husband is heterozygous for facial dimples and the wife
is without facial dimples.
2. In humans a bent little finger (5th digit) is dominant to a straight little finger (5th digit). Predict
the possible offspring of a couple where the husband and wife are both heterozygous for the
trait of a bent little finger (5th digit).
3. In humans a form of dwarfism (achondroplasia) is a dominant allele that causes short stature in
the heterozygous form and prenatal death in the homozygous state. Determine the probability
of a husband and wife who both have achondroplasia of having a child without the dwarfism
trait.
4. In humans, the presence of mid-digital hair on the fingers is dominant to having no hair on the
mid-digital finger area. The absence of hair on the fingers is recessive. Predict the possible
offspring produced by a husband, homozygous for mid-digital hair, and a wife who is
heterozygous for mid-digital hair.
5. In humans, a prominent chin cleft is dominant to a chin without a cleft. Predict the possible
offspring produced by a father without a chin cleft and a mother heterozygous for a chin cleft.
6. The “Achoo! Syndrome” is a condition where a person sneezes 2-3 successive sneezes when a
dark-adapted person suddenly is exposed to bright light. Having “Achoo! Syndrome” is
dominant to not having “Achoo! Syndrome.” Predict the possible offspring of a husband who
does not have “Achoo! Syndrome,” and a wife who is heterozygous for “Achoo! Syndrome.”
7. In humans, free ear lobes are dominant to attached ear lobes. Predict the possible offspring of a
husband with unattached ear lobes and a wife homozygous for free ear lobes.
8. In humans, hand clasping is a trait involving dominance. A person who unwittingly wraps the left
thumb on top of the right is dominant over a person who wraps the right thumb over the left
thumb. Predict the offspring of a husband and wife both heterozygous for left over right hand
clasping.