Deck 21: Genetic Analysis of Quantitative Traits

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.

Answer 1

E

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.

Answer 2

A

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.

Answer 3

C

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.

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.

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.

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

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

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

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.

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.

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

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

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

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

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.

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

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.

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

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.

Question 21

Which component of variance in a trait such as stamina in horses is the best indicator of whether the trait will respond to selection?

Question 22

While most additive polygenic traits show continuous distribution,some can be divided into two or more categories based on their contribution to genetic liability.Such traits are said to have what separation between affected and unaffected members of a population?

Question 23

What two measures describe the distribution of a trait in a sample?

Question 24

For a specific desirable trait in a breed of sheep,VP is 28.6,VC is 11,and VA is 7.2.What is its broad sense heritability?

Question 25

Which will exhibit the most shared maternal effects (uterine environment,etc.): identical or fraternal twins?

Question 26

Although a polygenic trait is influenced by the effect of several genes,one or more of these may be major genes;but many others with lesser effects are known as what type of gene?

Question 27

Of the variance and the standard deviation for a set of data about a trait,which represents the square of the difference between each of the values and the mean of the sample,divided by the degrees of freedom?

Question 28

Calculate the narrow sense heritability (h₂)for the following data on a trait in turkeys:
VA = 11.0
VE = 94.4
VP = 114.2
VD = 13.8

Question 29

If H₂ for club foot is estimated as 80%,would you expect a small difference such as 30 versus 27 between MZ and DZ twins,or a large difference,such as 30 versus 2?

Question 30

If the odds ratio for a particular QTL/DNA marker pair (e.g.,Q₁₀M₁₀)is 2.2,this indicates that the organism is how many times more likely to get Q₁₀M₁₀ gametes?

Question 31

What is the statistically acceptable Lod score that provides evidence of genetic linkage?

Question 32

After the location of a genome region likely to include a QTL,what must be found in this region?

Question 33

Sometimes the DNA marker allele and a QTL occur more frequently than would otherwise be expected,either because they interact or because of natural selection.What term describes this?

Question 34

A homozygous plant has sepals of 30-cm flowers while another homozygote of the same species has 40-cm flowers.The F₁ flowers are all 35 cm.In the F₂,out of 600 plants the smallest flowers were 30 cm and the largest were 45cm;all the others were of intermediate sizes.If all the genes involved in flower size are additive,how many gene pairs are there?

Question 35

A strain of a cereal grain can be either dark tan,medium-dark tan,medium tan,light tan,or cream colored.When a dark tan and a cream plant are crossed,all F₁ are medium tan.The F₂ are distributed in a ratio of 1:4:6:4:1 from darkest to lightest.How many genes are involved in this coloration?

Question 36

QTLs are most often mapped relative to DNA markers by using what scores as measurement?

Question 37

If we suppose that a specific QTL is genetically linked to a DNA marker at a recombination frequency of 10%,then the parental type combinations in gametes would be expected at what frequency?

Question 38

Of mean,median,and modal,what value is the most common value in a given population?

Question 39

A strain of a cereal grain can be either dark tan,medium-dark tan,medium tan,light tan,or cream colored.When a dark tan and a cream plant are crossed,all F₁ are medium tan.The F₂ are distributed in a ratio of 1:4:6:4:1 from darkest to lightest.How many additive alleles are needed to produce the darkest phenotypes?

Question 40

For the following traits,the concordance (occurrence of the same phenotype)of MZ and DZ twins are given as percentages.Which trait shows the most genetic as opposed to environmental influence?

Question 41

A GWA study relies on the correlation between a QTL and a ________.

Question 42

Given a list of the percentage of monozygotic and dizygotic twins in concordance for a selection of traits,describe how you would evaluate the relative input of environmental versus genetic factors.

Question 43

Many human behavioral traits have both genetic and environmental components.Bipolar disorder has long been known to be familial,and more recently a number of genes and/or SNPs have been found to be involved.What are three or more reasons that this research has been hampered?

Question 44

Recent work in Drosophila demonstrated that the genes known as the chromatin remodeling complex co-localize at loci for hsp genes that respond to heat shock.Outline a procedure you could use to substantiate this finding.

Question 45

If a trait results from genetic variation as well as environmental factors,it is known as a ________ trait.

Question 46

Distinguish between broad sense heritability and narrow sense heritability,and explain how either or both of these measures can be used to inform those using artificial selection.

Question 47

In some traits,different phenotypes result from genes whose alleles each contribute a specific increment to the whole.The phenotypes then have a ________ phenotypic distribution.

Question 48

If a trait results from the action of several genes,it is called a ________ trait.

Question 49

Describe how quantitative traits can be explained in Mendelian terms.

Question 50

What is meant by a QTL?