Question 1

Which of the following is NOT true of familial aggregation of a trait?&#10;A) One should compare the clustering of the trait in affected families compared to the general population&#10;B) Family clustering proves there is a genetic contribution to the trait&#10;C) Increased trait sharing in monozygotic compared to dizygotic twins suggests a genetic contribution to the trait&#10;D) Traits with a genetic liability will show familial aggregation&#10;E) These studies can be plagued by ascertainment bias

Accepted Answer

Familial aggregation suggests there may be a genetic contribution to a trait, but it does not prove it definitively. Other factors such as environmental or cultural influences may also be involved.

Question 2

Which model attempts to explain the etiology of discontinuous multifactorial traits?&#10;A) Random segregation model&#10;B) Hardy-Weinberg model&#10;C) Liability threshold model&#10;D) Additive trait model&#10;E) Multiplicative trait model

Accepted Answer

Discontinuous multifactorial traits are traits that exhibit a distinct and non-continuous distribution, such as the presence or absence of a disease. The liability threshold model attempts to explain the etiology of such traits by proposing that individuals have an underlying liability, or predisposition, to the trait which is influenced by multiple genetic and environmental factors. Once this liability threshold is crossed, the trait manifests in a discontinuous manner.

Question 3

For multifactorial traits,how would the liability threshold model predict that a second affected child in a family would alter risk estimates for future pregnancies?&#10;A) The risk estimate would increase&#10;B) The risk estimate would decrease&#10;C) The risk estimate would remain the same&#10;D) The chances would be exceedingly small that there would be a third affected child

Accepted Answer

The liability threshold model suggests that for multifactorial traits, there is a threshold level of liability that must be reached for the trait to be expressed. This means that having one affected child in a family increases the likelihood that other members of the family also have a higher liability level for the trait. Therefore, the risk estimate for future pregnancies would increase with the presence of a second affected child in the family.

Question 4

In a genetic association study,what does an odds ratio represent?&#10;A) The ratio of those with a particular allele who manifest a trait versus those with the allele who do not manifest the trait&#10;B) The risk of manifesting a trait in those with a particular allele compared to the risk of manifesting the trait in those without the allele&#10;C) The risk of the trait in those with the major allele versus the risk in those with the minor allele&#10;D) The genetic risk that you will have a particular trait versus the environmental risk that you will have the same trait&#10;E) The likelihood that someone with both genetic and environmental risks will express a trait versus the likelihood when they have neither risk

Accepted Answer

An odds ratio in a genetic association study represents the ratio of the risk of manifesting a particular trait in those with a particular allele compared to the risk of manifesting the trait in those without the allele. It is a measure of the strength of association between a genetic variant and a phenotype. It is calculated by dividing the odds of having the phenotype in those with the variant allele by the odds of having the phenotype in those without the variant allele.

Question 5

Compared to standard linkage analysis methods,what is an advantage of the affected sib pair method for gene hunting in complex traits?&#10;A) Smaller samples are required&#10;B) You can use two affected individuals from one family&#10;C) No model specification is required for the mode of inheritance&#10;D) Siblings who are discordant for the trait provide information for the analysis&#10;E) Fewer markers need to be genotyped

Accepted Answer

The affected sib pair method does not require a specific model for the mode of inheritance, making it advantageous for studying complex traits where the inheritance pattern is not well understood.

Question 6

One goal of the International HapMap project is to identify which of the following?&#10;A) Large families for linkage analysis&#10;B) The complete set of SNPs in the human population&#10;C) A genome-wide set of tag SNPs&#10;D) All possible haplotypes in the human population&#10;E) The complete genome sequence in a set of individuals from various regions of the world

Accepted Answer

The International HapMap project aims to create a genome-wide set of tag SNPs that can represent the majority of genetic variations in different populations. This helps reduce the cost and effort required for genotyping and association studies. The project does not aim to identify large families for linkage analysis (A) or all possible haplotypes in the human population (D). While the project uses SNP data, it does not aim to identify the complete set of SNPs in the human population (B) or the complete genome sequence of individuals (E).

Question 7

What is population stratification?&#10;A) Separation of a cohort into cases and controls&#10;B) Separation of a cohort by ethnicity&#10;C) A false positive association due to the presence of unrecognized subpopulations in a cohort&#10;D) The use of subsets of a cohort in both family-based and case-control association studies&#10;E) A false negative study due to heterogeneity in a cohort

Accepted Answer

Population stratification occurs when there is a presence of unrecognized subpopulations in a study cohort, leading to a false positive association between a trait and a genetic variant. This happens when cases and controls come from different populations with varying allele frequencies, leading to spurious associations.

Question 8

Multifactorial,quantitative traits often show which type of distribution in a population?&#10;A) Normal&#10;B) Uniform&#10;C) Bernoulli&#10;D) Random&#10;E) Bimodal

Accepted Answer

Multifactorial, quantitative traits are influenced by multiple genes and environmental factors, resulting in a continuous variation of phenotypes. This type of variation often shows a normal distribution in a population, where most individuals cluster around the mean and the frequency of extreme phenotypes decreases gradually towards the tails of the distribution.

Deck 9: Polygenic and Multifactorial Inheritance