Download Theoretical Genetics Practice Problems The allele for hemoglobin in

Theoretical Genetics Practice Problems
1. The allele for hemoglobin in sickle cell anemia (HbS) is only different by one base pair
from the allele for normal hemoglobin (HbA). To produce the sickle cell allele, at some
point in human history a mutation occurred in a gamete and the DNA sequence GAG
became GTG because of a base substitution mutation. This caused glutamic acid to be
replaced by valine in the protein sequence. This causes the hemoglobin molecule to be
misshapen, and therefore the entire erythrocyte to be sickle-shaped.
If a person is homozygous for the trait, they do not have sickle cell anemia. If the person
is homozygous for sickle cells, they have sickle cell anemia and are likely to die at an
early age. If, however, a person is heterozygous for the sickle cell trait, they have both
sickled and normal cells, and so can survive normally. The heterozygote is also resistant
to malaria and less likely to die from it.
Given this information, find out what the possible offspring there are when both parents
are heterozygous. Use this information to help you explain why sickle cell trait continues
to be present in the gene pool in some areas of the world, despite how terrible sickle cell
anemia is for people who have it.
2. A woman with type AB blood is caring for her elderly parents. As she is coordinating
their treatment with the doctor, she finds out her father has type A blood and her mother
has type O blood. From this information, she thinks she may be adopted. Use Punnett
squares to help you decide why she might come to this conclusion. Also, are there any
more explanations for what she has found?
3. Color blindness is a sex-linked trait. A woman is pregnant with a son. Her husband is
colorblind and so is her father, but none of her mother’s relatives ever have been. What
are the chances that her son will be colorblind? Use Punnett squares to help you fully
explain your answer.