Deck 22: The Genetics of Complex Traits

Question 1

Complex quantitative traits often show

A)only one discrete phenotype.
B)a distribution with a large proportion of individuals at the two extremes.
C)a normal distribution with an equal number of points above and below the mean.
D)a normal distribution with an equal number of points at each value within the range.

Answer 1

C

Question 2

To test for statistical significance of the association of a SNP with a trait, the null hypothesis in a chi-square test for independence is that the one of the SNP alleles is more common in the Cases than in the Controls.

Answer 2

False

Question 3

Typically, multiple interacting genes and the environment contribute to a complex quantitative trait, resulting in

A)discontinuous distribution of discrete phenotypes.
B)continuous variation of the trait in a population.
C)strict dominance of a single allele so that one phenotype is most common.
D)continuous variation of the trait in a single individual.

Answer 3

B

Question 4

The genetic relatedness of two siblings is

A)2.0.
B)1.0.
C)0.5.
D)0.25.
E)0.75.

Question 5

In a GWAS experiment, 500,000 SNPs across the genome are genotyped in thousands of Case and Control individuals.Which statistical analysis should be applied and why?

A)A chi-square test for goodness of fit will test the null hypothesis that the distribution of each SNP allele is the same in Cases and Controls.
B)A chi-square test for goodness of fit can be used because this is a small number of SNPs.
C)A chi-square test for independence should be used to test the null hypothesis that the distribution of each SNP allele is the same in Cases and Controls.
D)A chi-square test for independence should be used to test the null hypothesis that each SNP is linked to a QTL.

Question 6

When the results of a GWAS experiment using 500,000 SNPs are plotted in a Manhattan plot, significantly associated SNPs are

A)data points with a ‒log (p value)less than 0.05.
B)data points with a ‒log (p value)greater than 7.
C)data points with a ‒log (p value)greater than 7 that fall within a known coding sequence.
D)any data points above the line of correlation.

Question 7

Most complex quantitative traits

A)are affected by both genetic and environmental factors.
B)usually do not result in continuous phenotypes.
C)are not usually affected by environmental conditions.
D)usually result in one or two phenotypic values such as red or white eye color in Drosophila.

Question 8

Introgressions are used to

A)fine map QTLs.
B)establish linkage disequilibrium.
C)establish linkage equilibrium.
D)rough map QTLs.

Question 9

A SNP that can exist as a C or G is associated with a human disease.The genotypic odds ratio of the homozygote CC relative to the homozygote GG is 2.2, which indicates that

A)both CC and GG individuals are equally likely to get the disease because 2.2 is not a significant value.
B)heterozygotes are 2.2 times as likely to get the disease as GG homozygotes.
C)CC homozygotes are 2.2 times as likely to get the disease as GG homozygotes.
D)CC homozygotes are 2.2 times less likely to get the disease as GG homozygotes.

Question 10

In an experiment to distinguish genetic versus environmental effects on a trait, the test individuals

A)should be as genetically related as possible.
B)should have variable alleles at as many loci as possible.
C)must have the same parents.
D)must be grown in a natural environment.

Question 11

Twins from two individual zygotes (dizygotic twins)

A)are as related genetically as monozygotic twins.
B)share no genetic similarities.
C)are 100% genetically identical.
D)are as related genetically as non-twin siblings.

Question 12

The total phenotype variance (V_P)is

A)the sum of genetic variance (V_G)and environmental variance (V_E).
B)the difference between V_G and V_E.
C)independent of V_G.
D)independent of V_E.
E)always constant.

Question 13

Which of the following is not true about monozygotic twins?

A)They share all alleles at all loci.
B)They have a genetic relatedness of 0.5.
C)They have a genetic relatedness of 1.0.
D)They come from the joining of a single egg with a single sperm cell.
E)They are the result of a split of the zygote after fertilization.

Question 14

During truncation selection, the realized heritability of a trait depends on the selection differential, which is the difference between the average trait value of the selected parents and the average trait value of the entire parental population.

Question 15

By definition, linkage disequilibrium means that

A)alleles at separate loci occur together more than predicted by random chance.
B)alleles at separate loci segregate randomly.
C)two allelic variants are at least 60 m.u.apart.
D)two allelic variants are 50 m.u.apart.

Question 16

Broad-sense heritability is defined as

A)V_G.
B)V_P.
C)V_E.
D)V_G/V_P.
E)V_P/V_G.

Question 17

A SNP that can be either A or T is associated with a human disease.In the Case population, there were 2000 A alleles and 1500 T alleles.In the Control population, there were 2500 A alleles and 3000 T alleles.The allelic odds ratio indicates that the presence of an A confers a ________ times greater risk for the disease than does the T allele.

A)1.33
B)1
C)0.64
D)1.6

Question 18

A farmer performs truncation selection to try to increase the weight of peaches in his orchard.Which statement correctly describes a possible outcome of this selection?

A)If peach weight is not heritable, the average weight in the next generation will increase.
B)If peach weight is heritable, the average weight in the next generation will increase.
C)The average peach weight will decrease due to this inbreeding.
D)If peach weight is heritable, the average weight in the next generation will decrease.

Question 19

If a trait is heritable, then individuals with a genetic relatedness of 0.5 are expected to

A)exhibit more phenotypic similarity than two random individuals in the population.
B)be as similar in phenotype as a pair of random individuals in the population.
C)have identical phenotypes because they are twins.
D)have an average phenotypic value that is close to the mean of the population.