Deck 14: Molecular and Genetic Epidemiology

Question 1

Consider a disease with two alleles, B and b. List all of the mating types that could produce a heterozygous child.

Answer 1

A child is considered heterozygous when its cells comprise two dissimilar alleles of a specific gene. For a disease that involves two alleles, B and b, a heterozygous child would be Bb.The subsequent mating types would produce a Bb heterozygous child:
• Bb BB
• Bb Bb
• Bb bb
• BB bb

Question 2

For the situation described in problem 1, which mating type gives the highest proportion of heterozygous offspring?

Answer 2

A child is considered heterozygous when its cells comprise two dissimilar alleles of a specific gene. For a disease that involves two alleles, B and b, a heterozygous child would be Bb.Among the subsequent mating categories:
• Bb BB
• Bb Bb
• Bb bb
• BB bb would produce the highest proportioned heterozygotes at 100%.

Question 3

It is impossible for you to have received a sex chromosome from one of your four grandparents. Which grandparent could not have transmitted, via your parents, a sex chromosome to you? Answer as if you were (a) male and (b) female.

Answer 3

(a)For the first situation, refer to below:
1. X a X a X b Y b = X a Y b
2. X a Y b X c X c = X a X c
Therefore, a female receives no sex chromosome from her father's father (X b Y b ).
(b)For the second situation, refer to below:
1. X a X a X b Y b = X a Y b
2. X a Y b X c X c = X c Y b
Therefore, a male receives no sex chromosome from his father's mother (X a Y a ).

Question 4

A case-control study of multiple sclerosis (MS) was conducted in which family history of MS was collected on all first- and second-degree relatives. Among the 500 cases, 16 reported an affected relative. Among the 500 age- and sex-matched controls, 8 reported an affected relative. Do these data suggest a familial component to MS?

Question 5

For a disease with an adult age at onset, what is the rationale for matching cases and controls on age when one is most interested in family history of the disease?

Question 6

You are interested in determining whether or not there is a genetic predisposition to lung cancer. Provide at least five reasons why lung cancer might cluster in a family for nongenetic reasons.

Question 7

A published segregation analysis of asthma shows that all Mendelian patterns of inheritance do not provide a good fit to the data compared with the general model. Does this rule out the possibility that genes influence risk of asthma?