Jorde: Medical Genetics, 5th Edition
Chapter 2: Basic Cell Biology: Structure and Function of Genes and Chromosomes
Sample Problems & Essay Questions
Question 1: In some African populations, the prevalence of sickle cell disease, an
autosomal recessive condition, is 1/100. Based on this value, what proportion of the
population would be heterozygous carriers of the sickle cell disease gene?
Answer: q = 0.1 p = 0.9 2pq = 0.18
Question 2: If an X-linked dominant disorder affects 1/100 males in a population, what
is the gene frequency for the disorder in the population?
Question 3: In the population in question 2 (an X-linked dominant disorder affects 1/100
males in a population), what proportion of females would be affected with the X-linked
Answer: q^2 + 2pq = ~2q = 0.02 = 1/50
Question 4: A man who is affected with hemophilia A (X-linked recessive) mates with a
woman who is a heterozygous carrier of this disorder. What proportion of this couple’s
daughters will be affected, and what proportion of the daughters will be carriers?
Answer: 0.50; 0.50
Question 5: A man who has Neurofibromatosis type 1 (autosomal dominant) marries a
phenotypically normal woman. If they have five children, what is the probability that
none of the children will be affected with this disorder? What is the probability that all of
the children will be affected?
Answer: (1/2)^5 = 1/32
Question 6: You have ascertained a fully penetrant autosomal dominant disease
condition in three offspring of a couple with no family history of the disorder. What is the
most likely explanation for the pedigree shown here?