Question 1

Which of the following best describes the main difference between family-based linkage analysis and population association studies in identifying risk alleles for complex diseases?

Accepted Answer

Family-based linkage analysis identifies rare variants with large effects, while population association studies are more powerful for common variants with small effects.

Question 2

In the context of the threshold model for discrete diseases, what does the 'threshold' represent?

Accepted Answer

A liability value above which an individual is affected by the disease.

Question 3

A trait is controlled by two loci, each with two alleles (A/a and B/b). If environmental variation is present, which of the following best describes the expected phenotypic distribution?

Accepted Answer

A multi-modal distribution that becomes more continuous as environmental variation increases.

Question 4

Which equation correctly represents the calculation of power in an association study, considering the effect size (GRR) and risk allele frequency ($p$)?

Accepted Answer

$	ext{Power} = 1 - \beta$

Question 5

In an affected sib pair analysis, what does 'identity by descent' (IBD) mean?

Accepted Answer

Siblings inherit the same allele from a common ancestor at a specific locus.

Question 6

Which of the following best explains why linkage disequilibrium (LD) can be used to map disease genes in founder populations?

Accepted Answer

Founder populations have reduced recombination, preserving long haplotype blocks around disease alleles.

Question 7

A haplotype block is best defined as:

Accepted Answer

A segment of DNA with limited diversity and strong linkage disequilibrium among variants.

Question 8

In a genome-wide association study (GWAS), what does a Manhattan plot display?

Accepted Answer

The $-\log_{10}(P)$ values of association tests for SNPs across the genome.

Question 9

If a risk allele has a frequency of $p = 0.5$ and a genotype relative risk (GRR) of 2.0, what can be inferred about the power to detect association in a well-powered study?

Accepted Answer

Power will be high because both the allele frequency and effect size are optimal.

Question 10

Which of the following is a common misconception about the use of cluster plots in genotype calling?

Accepted Answer

Cluster plots are only useful for qualitative traits.

Question 11

A researcher observes that two SNPs have a $D'$ value of 0.95. What does this indicate about the relationship between these SNPs?

Accepted Answer

They are in strong linkage disequilibrium and rarely recombine.

Question 12

Which of the following best describes the effect of increasing environmental variation on the phenotypic distribution of a polygenic trait?

Accepted Answer

It creates a more continuous, bell-shaped distribution.

Question 13

In the context of the HLA region, why is it challenging to map disease genes using standard association methods?

Accepted Answer

The HLA region exhibits extensive linkage disequilibrium and high polymorphism.

Question 14

Which of the following statements about linkage disequilibrium (LD) is correct?

Accepted Answer

LD refers to the non-random association of alleles at different loci.

Question 15

A GWAS identifies a SNP with a $P$ value of $1 	imes 10^{-8}$. What does this indicate?

Accepted Answer

There is a strong statistical association between the SNP and the trait.

Question 16

Which of the following scenarios would most likely result in a false positive in a population association study?

Accepted Answer

Population stratification leading to allele frequency differences unrelated to disease.

Question 17

If two siblings share one allele IBD at a locus, what is the probability that they are both affected by a recessive disease caused by a mutation at that locus?

Accepted Answer

Greater than if they share zero alleles IBD.

Question 18

Which of the following best explains why haplotype blocks are useful in association studies?

Accepted Answer

They allow researchers to genotype fewer SNPs while capturing most genetic variation.

Question 19

A population has limited chromosome diversity in a haplotype block. What is the most likely explanation for this observation?

Accepted Answer

Recent positive selection or a population bottleneck has reduced diversity.

Genetic Approaches to Identifying Risk Alleles for Complex Disease

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