Question 1

A group that is experimenting with selection in an insect species due to exposure to a newly developed insecticide,cpd AW143,has found that,after 10 generations of exposure,the population is now bimodal in its response to the drug.Close to 30% of the population are completely normal while 70% live only about 1/6 of the normal lifetime.This is an example of
A)threshold effect.
B)stabilizing selection.
C)additive genes.
D)directional selection.
E)disruptive selection.

Accepted Answer

This is an example of disruptive selection as the population is splitting into two distinct groups with different responses to the insecticide. The 30% that remain normal and the 70% that have a significantly reduced lifespan are clearly different from each other, indicating a divergence in their response over time.

Question 2

GWA looks at DNA marker distribution relative to that of supposed QTLs.Therefore,which of the following would be true of linkage disequilibrium?
A)There is a higher frequency association between marker and a QTL.
B)The GWA score is lower than expected.
C)The Lod score is negative.
D)It is found in a highly inbred strain.
E)It is increased in homozygous individuals.

Accepted Answer

Linkage disequilibrium refers to the non-random association of alleles at two or more loci, due to their physical proximity on the same chromosome. In the context of GWA, if there is a high frequency association between a marker and a QTL, it indicates that they are physically close, and therefore, there is a higher likelihood of detecting an association between them in a GWA analysis. This would result in a higher GWA score, making choice B incorrect. Lod score is a measure of linkage, not disequilibrium, making choice C incorrect. Linkage disequilibrium is not limited to inbred strains (choice D), and while it can be increased in homozygous individuals, it can also exist in heterozygotes. Therefore, A is the best choice.

Question 3

Alterations in the ratio of CD4:CD8 lymphocytes are associated with risk of HIV infection progressing to AIDS,of autoimmune diseases,and of progression of some cancers.In searching for predictors of these effects in normal individuals,researchers have found two independent QTLs in the region of the genome known as the major histocompatibility complex (MHC),one in a region regulating CD8 and the other in a region regulating CD4.What does this indicate for the general population?
A)Mutation in one or both of these genes causes HIV and AIDS.
B)Autoimmune diseases such as type 1 diabetes are caused by one of these genes.
C)Variation in one or the other of these genes may increase the risk of autoimmune diseases.
D)Only one mutation can be the cause of rheumatoid arthritis.
E)The probability of an autoimmune disease demonstrates that additive genes are involved.

Accepted Answer

The presence of two independent QTLs (quantitative trait loci) in the region of the genome known as the major histocompatibility complex (MHC), one in a region regulating CD8 and the other regulating CD4 indicates that variation in one or the other of these genes may increase the risk of autoimmune diseases. This correlation does not imply causation but suggests that these QTLs may be useful predictors of autoimmune disease risk in normal individuals.

Question 4

An increased number of patients have recently been diagnosed with celiac disease,which you may know of as gluten sensitivity (OMIM 212750).It is a multifactorial disorder of the small intestine influenced by genes and environment,and it is characterized by malabsorption due to inflammation of the mucosa after eating wheat gluten or related proteins.It is now thought to occur in 1 out of 120 to 300 people.Genes found to be associated with it are in the HLA region of chromosome 6,namely DR3 and DQw2.Which of the following is more probable?
A)It is an autoimmune disorder.
B)It is caused by exposure to gluten in infancy.
C)It has high broad-sense heritability.
D)Its frequency varies greatly by population.
E)It is found primarily in inbred populations.

Accepted Answer

The answer of An increased number of patients have recently...

Question 5

It is estimated that 4.6% of SNPs and about 17% of all genes can be defined as pleiotropic.Which of the following might be a significant lesson for a consumer of genetic information based on this finding?
A)A test identifying a gene for a disease might actually be a test for a different disorder instead.
B)Any variant that we gain information about might in the future be found to associate with a more stigmatizing condition.
C)A physician might be treating the major condition but not notice even more deleterious outcomes.
D)The classification of my genetic disorder might be incorrect.
E)Sequencing of the candidate gene might find the wrong expected functional significance.

Accepted Answer

The answer of It is estimated that 4.6% of SNPs...

Question 6

Although no specific gene alteration has yet been demonstrated as a cause for schizophrenia (SZ),it is known to have a strong genetic component.A recent study has found a strong association between SZ and a locus at chromosome 10q22-23 in Ashkenazi Jewish and Taiwanese Han populations.Which of the following is probable?
A)Other populations will have the same association with 10q22-23.
B)The neuregulin-3 gene at this locus is mutated in all or most SZ cases.
C)SZ exhibits significant genetic heterogeneity in different populations.
D)The region on 10q must include several genes associated with SZ.
E)People with SZ being characterized differently in various medical communities results in this association between the Jewish and Han populations.

Accepted Answer

The fact that the association between SZ and the 10q22-23 locus has only been found in Ashkenazi Jewish and Taiwanese Han populations suggests that SZ exhibits significant genetic heterogeneity in different populations. This means that different populations may have different genetic factors contributing to the development of SZ.

Question 7

Once a chromosomal position for a putative gene associated with Parkinson disease is verified,which of the following is a next step?
A)developing a FISH screening test to identify pre-Parkinson patients
B)determining whether this locus is mutated in all Parkinson patients
C)using a genome-wide linkage SNP panel to identify more minor genes
D)ascertaining all living and at-risk individuals who are family members of the affected test subjects
E)fine mapping of the linkage region to identify particular variants for influencing risk

Accepted Answer

Fine mapping of the linkage region to identify particular variants for influencing risk would be the next step. This would involve analyzing the specific variations in DNA sequence within the identified chromosomal position to determine which variants are associated with an increased risk of developing Parkinson disease. This information can be used to develop more targeted treatments and diagnostic tests for the disease. The other options listed may be relevant at later stages of research, but fine mapping is the immediate next step for identifying specific genetic variants associated with Parkinson disease.

Question 8

A hypothetical condition in some domesticated fowl is identified phenotypically by patchy loss of feathers on the animals' backs.Although several factors,genetic and environmental,are found to be involved,only about 3% of any population with any of these factors are found with feather loss.Which of the following is a likely cause?
A)continuous variation
B)threshold of liability
C)low mutation frequency
D)high number of alleles in one of the genes
E)high number of environmental effects

Accepted Answer

The fact that only about 3% of the population with any of the involved factors are found with feather loss suggests a threshold of liability, meaning that the condition only manifests if a certain level of exposure to the factors is reached.

Question 9

If you know the proportion of F₂ individuals that are of parental phenotypes,what formula will tell you how many gene pairs are influencing the trait?
A)1/4ⁿ
B)N¹/⁴
C)VE + Vg
D)H²/h²
E)2n + 1

Accepted Answer

The proportion of F₂ individuals that are of parental phenotypes can be used to determine the number of gene pairs influencing the trait through the formula 1/4ⁿ, where n is the number of gene pairs involved in the trait. The parental phenotypes occur when the F₁ individuals are heterozygous for the trait, which means that the ratio of genotypes in the F₂ generation will be 1:2:1 (homozygous dominant:heterozygous:homozygous recessive), or 3/4 dominant and 1/4 recessive. In the case of parental phenotypes, the ratio is 3:1, which is 1/4 of the total. Thus, if the proportion of parental phenotypes is known, the number of gene pairs can be determined using the formula 1/4ⁿ.

Question 10

As an H²value approaches 0.0,which of the following must be true?
A)Almost all of the phenotype is VG.
B)Almost all of the phenotype is VE.
C)Identical (MZ)twins are virtually all discordant.
D)Fraternal (DZ)twins are virtually all concordant.
E)h² = VA/VP.

Accepted Answer

As H²value approaches 0.0, almost all of the phenotype becomes VE (environmental contribution) and very little VG (genetic contribution) is left. This means that the variation in the phenotype is mostly due to environmental factors rather than genetic factors.

Question 11

It is clearly established that obesity has greatly increased in children over the last several decades in the United States.While several genes have been identified that increase the potential for obesity,environmental influences are also involved.Which of the following is most likely?
A)There is little or no gene-environment interaction.
B)Phenotypic variation is discontinuous.
C)There is a small overlap of phenotypic ranges of different genotypes.
D)There is a wide range of phenotypes with each genotype.
E)There is a demonstrable threshold of environmental effects.

Accepted Answer

The statement that "environmental influences are also involved" suggests that there is some variability in the expression of obesity across different individuals with the same genotype. This points towards a wide range of phenotypes with each genotype (option D), rather than little to no gene-environment interaction (option A), discontinuous variation (option B), small overlap of phenotypes (option C), or a demonstrable threshold of environmental effects (option E).

Question 12

Which of the following best predicts the response of a trait to artificial selection?
A)VA
B)VG
C)H²
D)h²
E)standard deviation

Accepted Answer

The narrow-sense heritability (h²) best predicts the response of a trait to artificial selection, as it measures the proportion of phenotypic variance that is due to additive genetic variance, which is directly passed from parents to offspring.

Question 13

Until recently,only apolipoprotein E (APOE)polymorphisms have been found to correlate with late-onset (nonfamilial)Alzheimer disease (AD);however,these account for less than 50% of the VG.New GWA studies have found a chromosome 12 risk locus.What method will likely be used by AD researchers going forward?
A)assessment of chromosome 12 for areas of linkage disequilibrium for AD
B)association of APOE alleles with chromosome 12 SNPs
C)sequencing of candidate genes on chromosome 12 and search for sequence similarity
D)genotyping of a large cohort of AD patients and matched controls using a microchip
E)analysis of genotypes of a large number of AD patients who have none of the expected APOE alleles

Accepted Answer

Genotyping of a large cohort of AD patients and matched controls using a microchip is the most likely approach that AD researchers will use going forward. This method allows for the detection of genetic variations across the whole genome, rather than focusing on a specific locus or candidate genes. It also allows for the comparison of AD patients with matched controls to identify genetic variants that are more common in AD patients than in controls.

Question 14

A recent study investigated the heritability of lean body mass (LBM)that had been previously reported as between 52 and 84% but without known specific genes.The authors used a genome-wide association (GWA)scan to identify two SNPs: rs16892496 and rs7832552 within the thyrotropin-releasing hormone receptor gene that were significantly associated with LBM.Since the gene in question involves muscle metabolism,which of the following would you predict would be associated with LBM in a given population?
A)high LBM associated with higher risk of fracture in the elderly
B)high LBM associated with memory loss in the middle aged
C)low LBM associated with mobility limitation in the elderly
D)low LBM associated with the growth spurt of puberty
E)variation of LBM for members of different geographic populations

Accepted Answer

The gene identified through the GWA scan is involved in muscle metabolism, so it would be reasonable to predict that variations in LBM might affect mobility. Option A and B do not have any biological plausibility, while option D is not related to the given gene. Option E may be possible, but since the question is asking for a prediction within a single population, it is less relevant.

Question 15

Which of the following is most typical of a case of quantitative inheritance?
A)a ratio of 9:3:3:1
B)continuous variation in phenotypes
C)discontinuous variation in genotypes
D)lack of a clearly dominant phenotype
E)a trait with little to no genetic influence

Accepted Answer

Continuous variation in phenotypes is the most typical of a case of quantitative inheritance. This means that the trait is controlled by multiple genes and environmental factors, and results in a range of phenotypes that fall along a spectrum rather than distinct categories. Examples of traits that exhibit quantitative inheritance include height, weight, and intelligence. The other answer choices are not characteristic of quantitative inheritance - a ratio of 9:3:3:1 is indicative of Mendelian inheritance, discontinuous variation in genotypes suggests distinct categories of traits, lack of a clearly dominant phenotype suggests incomplete dominance or codominance, and a trait with little to no genetic influence would not exhibit quantitative inheritance.

Question 16

Mean platelet volume (MPV)in humans increases with heart attacks and strokes and is used to predict recurrence as well as mortality.MPV has high heritability.A recent GWA study found MPV to be associated with three SNPs on chromosomes 12,3,and 17 respectively.These three QTLs accounted for 4-5% of MPV variance.Which of the following is a reasonable explanation?
A)Other loci may also account for significant variance of MPV.
B)These SNPs must be translocated or transposed alleles.
C)Monitoring of these SNPs should identify those at highest risk.
D)The three SNPs,when sequenced,should show high conservation.
E)The three SNPs will be found in genes responsible for stroke.

Accepted Answer

Since the three QTLs identified in the GWA study only account for 4-5% of MPV variance, it is likely that other loci also contribute to MPV variation.

Question 17

Parkinson disease (PD)is a neurodegenerative disease that has been associated with a significant number of different genes,therefore showing it to be genetically heterogenic.One recent study in 278 families found evidence of two such possible loci.Evidence for linkage to chromosome 18q11 was presented by Gao et al.in 2009.Which of the following would be considered reputable evidence for this?
A)lack of quantitative difference for the occurrence of both in individuals
B)use of persons from multiple ethnic and geographic backgrounds in the study
C)finding the locus to be in Hardy-Weinberg equilibrium in the population
D)finding the Lod score for association between the chromosomal location and PD to be 4.1
E)analysis of all other possible SNPs with no such association to chromosome 18

Accepted Answer

Finding a Lod score of 4.1 suggests strong evidence of linkage between the chromosomal location and PD. This indicates that the probability of observing the data if the linkage is true, compared to it being false, is high (at least 10,000:1). Choices A, B, C, and E are not relevant or appropriate measures of evidence for linkage to a specific chromosomal location.

Question 18

If lean body mass (LBM)and SNPs in the gene for a G-coupled receptor for a hormone secreted by the hypothalamus are associated,and the binding of this hormone is the first step in the release of thyroxin (necessary for skeletal muscle development),then increases in mutations in the hormone receptor gene would be expected to
A)increase LBM.
B)increase secretion by the hypothalamus.
C)decrease all thyroxin-mediated function.
D)increase body mass index (BMI).
E)alter the QTLs involved.

Accepted Answer

Mutations in the hormone receptor gene could impair the binding of the hormone, reducing thyroxin release and thus decreasing thyroxin-mediated functions, including skeletal muscle development.

Question 19

An animal breeder asks your advice about which of a number of traits could most effectively be selected for in his herd.Which would you most correctly suggest?
A)a trait with high VE
B)a high VA relative to VP
C)a high VP relative to VG
D)a low h² value
E)a low selection coefficient

Accepted Answer

A high VA relative to VP indicates that a large proportion of phenotypic variation is due to genetic variation, making it more likely that selection for that trait will lead to greater improvement in that trait in the next generation.

Question 20

QTL mapping resembles linkage analysis primarily because
A)it uses statistics to analyze its data.
B)it uses the location of a known DNA marker.
C)it uses the three-point mapping method.
D)the distances are reported in cM.
E)the results are quantifiable.

Accepted Answer

QTL mapping and linkage analysis both use the location of DNA markers to identify the location of traits on chromosomes. Therefore, choice B is the best choice as it correctly identifies the commonality between the two methods. Although the other options may also be true, they do not best describe the commonality between QTL mapping and linkage analysis.

Quiz 21: Genetic Analysis of Quantitative Traits

GWA looks at DNA marker distribution relative to that of supposed QTLs.Therefore,which of the following would be true of linkage disequilibrium?

It is estimated that 4.6% of SNPs and about 17% of all genes can be defined as pleiotropic.Which of the following might be a significant lesson for a consumer of genetic information based on this finding?

Once a chromosomal position for a putative gene associated with Parkinson disease is verified,which of the following is a next step?

If you know the proportion of F₂ individuals that are of parental phenotypes,what formula will tell you how many gene pairs are influencing the trait?

As an H²value approaches 0.0,which of the following must be true?

It is clearly established that obesity has greatly increased in children over the last several decades in the United States.While several genes have been identified that increase the potential for obesity,environmental influences are also involved.Which of the following is most likely?

Which of the following best predicts the response of a trait to artificial selection?

Which of the following is most typical of a case of quantitative inheritance?

An animal breeder asks your advice about which of a number of traits could most effectively be selected for in his herd.Which would you most correctly suggest?

QTL mapping resembles linkage analysis primarily because