Deck 17: Quantitative Genetics

Question 1

A QTL:

A)is one of the genes that influences a trait.
B)is a chromosomal region containing genes that influence a quantitative trait.
C)will not contain any genes other than the ones influencing a trait.
D)is a measure of the phenotypic variation in a quantitative trait.
E)is a measure of the genetic variation in a quantitative trait.

Answer 1

B

Question 2

The estimated broad-sense heritability for milk production in a herd of dairy cattle is high.Which is a valid inference?

A)Most of the variation in milk production in the herd is due to additive genetic variance within the herd.
B)Most of the variation in milk production in the herd is due to dominant genetic variance.
C)Little of the variation in milk production is due to environmental variation within the herd.
D)Selective breeding for high milk production in this herd will be effective.
E)Broad-sense heritability for milk production will be high in most other herds of dairy cattle.

Answer 2

C

Question 3

_____ is also called the average.

A)Mean
B)Standard deviation
C)Variance
D)Correlation coefficient
E)Narrow-sense heritability

Answer 3

A

Question 4

Suppose that researchers estimate that broad-sense heritability of IQ in Sweden is 0.8.Which of the following conclusions is valid, assuming that the estimate is accurate?

A)Most variance for IQ in Sweden is due to total genetic variance.
B)In Sweden, the environment does not play a large role in determining the IQ of individuals.
C)Enriching the environment of poor children in Sweden would not lead to a big improvement on IQ tests.
D)Broad-sense heritability of IQ in the United States probably is close to 0.8.
E)If another country has a lower broad-sense heritability for IQ, then this difference must be genetically based.

Question 5

In a normal distribution, 99% of the measurements fall within _____ of the mean.

A)1%
B)5%
C)plus or minus 1 standard deviation
D)plus or minus 2 standard deviations
E)plus or minus 3 standard deviations

Question 6

Phenotypic variation in a trait is often represented as a _____, which graphs the number of each phenotypic class in a sample.

A)bimodal distribution
B)frequency distribution
C)regression line
D)correlation
E)variance plot

Question 7

When _____ is high for a particular trait, offspring tend to resemble their parents for that trait.

A)phenotypic variance
B)the number of genes controlling a trait
C)narrow-sense heritability
D)genetic-environment interaction
E)environmental variance

Question 8

Heritability indicates the:

A)degree to which a characteristic is genetically determined.
B)proportion of phenotypic variation in a trait that is due to genetic differences.
C)degree to which a characteristic is environmentally determined.
D)proportion of phenotypic variation in a trait that is due to the environment.
E)extent to which identical twins are phenotypically similar.

Question 9

The _____ is the statistic that measures the spread of a distribution around the mean.

A)covariance
B)correlation coefficient
C)regression coefficient
D)variance
E)average

Question 10

Which of the following traits is a meristic trait?

A)Blood pressure
B)Fat content of milk in cows
C)Number of kittens in a litter
D)Tail length in mice
E)Oil content of corn kernels

Question 11

Quantitative characters often exhibit a _____ distribution.

A)skewed
B)normal
C)bimodal
D)covariance
E)tangential

Question 12

_____ can cause a single genotype to produce a range of potential phenotypes.

A)Epistasis
B)Genetic variance
C)Threshold effects
D)Environmental effects
E)Heritability

Question 13

Flower diameter in sunflowers is a quantitative trait.A plant with 6-cm flowers, from a highly inbred strain, is crossed to a plant with 30-cm flowers, also from a highly inbred strain.The F₁ have 18-cm flowers.F₁ × F₁ crosses yield F₂ plants with flowers ranging from 6 to 30 cm in diameter, in approximately 4-cm intervals (6, 10, 14, 18, 22, 26, 30). An 18-cm F₁ plant is crossed to a 6-cm plant.What is the probability of an offspring with one additive allele, if all genes that influence this trait are unlinked?

A)1/3
B)1/4
C)1/6
D)3/8
E)1/16

Question 14

Distributions A and B in the figure below have:

A)the same mean and the same variance.
B)different means and different variances.
C)the same mean but different variances.
D)different means but the same variance.
E)different means but are correlated.

Question 15

All of the following statements about heritability are true EXCEPT:

A)measures of heritability are specific to a defined population in a given environment.
B)the heritability of an individual cannot be estimated.
C)if heritability for a trait is high in a particular population, improving the environment is unlikely to result in a significant improvement in the trait over time.
D)heritability does not indicate the degree to which a characteristic is genetically determined.
E)heritability says nothing about the nature of differences between populations in a characteristic.

Question 16

Knowing the _____ of a trait has great practical importance because it allows statistical predictions regarding the phenotypes of offspring to be made on the basis of the parents' phenotypes.

A)variance
B)inbreeding coefficient
C)heritability
D)genotype
E)mean

Question 17

Unlike most examples of this trait, the height characteristic that Mendel studied in pea plants exhibited _____ variation.

A)continuous
B)discontinuous
C)meristic
D)threshold
E)quantitative

Question 18

_____ is a way to measure the strength of the association between two variables.

A)Regression
B)Covariance
C)Correlation
D)Variance
E)Standard deviation

Question 19

Which of the following traits is NOT a continuous trait?

A)Human height
B)Blood pressure
C)Oil content in corn kernels
D)Pea plant height studied by Mendel
E)Fat content of milk in cows

Question 20

A series of experiments shows that oil content in a diploid grain is influenced by five genes (a through e)with additive alleles.The highest producing strain is 20% oil content; the lowest has close to 0%.A plant of unknown genotype has an oil content of 12%.What is a possible genotype for this plant? (+ = additive alleles)

A)a⁺a⁺b⁺b⁺c⁺c⁺d⁺de⁺e
B)a⁺a⁺b⁺b⁺ ccddee
C)a⁺a⁺b⁺bccddee
D)aab⁺bc⁺cd⁺d⁺e⁺e⁺
E)a⁺a⁺b⁺b⁺c⁺c⁺d⁺dee

Question 21

Cloning is a procedure by which exact genetic duplicates are made.A litter of cloned rabbits was born from a single surrogate mother rabbit.Despite being genetically identical, each of the baby rabbits looked very different from one another.Explain in detail why this might have occurred.

Question 22

You and a close friend from the University of Tennessee go hiking in the mountains.You are surprised to see a salamander that is bright orange in color.Thinking that some overzealous Tennessee fans have painted this particular amphibian, you walk on.As you continue your hike, you find other salamanders of this species and note that there is variation in the coloration: some individuals are bright orange, but others are drab in color.You also note that these salamanders often eat bright orange insects.How might you explain the presence of the color polymorphism in this salamander species?

Question 23

Is it possible for a trait to be discontinuous and yet determined by multiple genetic and environmental factors? Explain.

Question 24

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants, with red kernels, heterozygous at both loci, are crossed, what fraction of the offspring is expected to have phenotypes distinct from parental?

A)1/16
B)4/16
C)6/16
D)10/16
E)All the offspring will have parental phenotypes.

Question 25

Do the principles discovered by Mendel for discontinuous traits also apply to the inheritance of traits that exhibit continuous variation? Explain your answer.

Question 26

Total phenotypic variance can be broken down into all but one of which of the following components?

A)Genetic-environment interaction variance
B)Genetic variance
C)Environmental variance
D)Heritability
E)Genic interaction variance

Question 27

Recently, genome-wide association studies that locate genes influencing quantitative traits have been facilitated by the use of:

A)pedigrees.
B)controlled crosses.
C)clonal lineages.
D)RFLPs.
E)SNPs.

Question 28

The model which best explains the inheritance of complex traits, such as height, weight, and IQ, attributes the control of the traits to:

A)a single gene with dominant and recessive alleles.
B)two genes with independent assortment.
C)more than one gene with no effect of the environment.
D)more than one gene plus environmental effects.
E)environmental factors and not genetic factors.

Question 29

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants, one with dark red kernels (+++- genotype), and one with light red kernels (+- - - genotype), are crossed, what fraction of the offspring is expected to have phenotypes distinct from parental colors?

A)1/4
B)4/16
C)6/16
D)1/2
E)10/16

Question 30

A population may eventually stop responding to artificial selection because:

A)individuals in the population have become homozygous for the alleles responsible for the trait.
B)natural selection opposes any further change in the characteristic.
C)natural selection can no longer enhance the results of artificial selection.
D)individuals in the population have become homozygous for the alleles responsible for the trait and natural selection opposes any further change in the characteristic.
E)individuals in the population have become homozygous for the alleles responsible for the trait and natural selection can no longer enhance the results of artificial selection.

Question 31

Suppose that a study of college students in Sweden estimates heritability of IQ to be 0.8.Based on this evidence, a school board in a struggling urban school district in the United States concludes that improving teaching methods and the physical conditions of schools is useless because intellectual achievement is determined almost entirely by genes and relatively little by the educational environment.Critique this conclusion based on your understanding of heritability.

Question 32

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants with red kernels, heterozygous at both loci, are crossed, what fraction of the offspring is expected to have phenotypes the most distinct from parental color?

A)1/16
B)2/16
C)4/16
D)6/16
E)10/16

Question 33

Cleft palate is a birth defect in which the two sides of the roof of the mouth do not fuse before birth.Cleft palate is considered to be a threshold trait.Define "threshold trait" and explain how cleft palate is an example of one.

Question 34

Estimates of heritability made by comparing related individuals assume that the environments of related individuals:

A)are more similar than those in which unrelated individuals are raised.
B)are not any more similar than those in which unrelated individuals are raised.
C)are manipulated so that some sibs within each family experience either one of the extreme ends of the environmental range.
D)have no effect at all on phenotypic variance in the family.
E)are identical for every sib in the family.

Question 35

A certain disease phenotype is a threshold trait, where disease occurs only if the number of susceptibility alleles in a genotype exceeds 3.How many phenotypic categories can be observed if the number of quantitative susceptibility loci has been determined as 5?

A)2
B)3
C)5
D)8
E)11

Question 36

The graph below shows how yield in two varieties of corn respond to different environmental conditions.Which statement below is TRUE?

A)Under tested conditions, variety 1 has a higher yield than variety 2.
B)Under tested conditions, variety 2 has a higher yield than variety 1.
C)Under tested conditions, variety 2 is more sensitive to environment quality than variety 1.
D)Variety 1 is genetically superior to variety 2.
E)Variety 2 is genetically superior to variety 1.

Question 37

Genetic variance is comprised of all of the following components EXCEPT:

A)additive genetic variance.
B)dominance genetic variance.
C)broad-sense heritability.
D)genic interaction variance.
E)None of the answers is correct.

Question 38

The height of a type of bean plant is determined by five unlinked genes called A, B, C, D, and E.Each gene has two alleles: additive (uppercase letter)and nonadditive (lowercase letter).The shortest plants are 130 cm.The tallest plants are 220 cm.
a.Estimate how many centimeters each allele contributes to the height difference of 90 cm.
b.The genotypes are known for two bean plants.Plant 1 is genotype AABbccDdEE.Plant 2 is genotype aaBBCcDdEE.What are their heights?
c.If the two plants in the previous question are crossed, could they produce a plant that is taller than either parent? How?
d.All the genes are unlinked.Determine the probability of an AbcdE gamete from plant 1, and an aBcdE gamete from plant 2.What will be the genotype and phenotype of a plant from these gametes, and what is the probability of a plant with this genotype?
e.If the progeny plant from the cross in the previous question was only 60 cm because of an allele in a gene other than A-E, what genetic phenomena are at work?
f.If the progeny plant with the genotype in part (d)was a few centimeters taller than your prediction, how would you explain it?

Question 39

_____ measures the effect of alleles at a locus interacting in a non-additive fashion.

A)Additive genetic variance
B)Dominance genetic variance
C)Genetic variance
D)Genetic-environment interaction variance
E)Phenotypic variance

Question 40

A study was conducted to investigate the levels of calcium and growth hormone excreted in chicken dung on a major chicken farm.The variances (V)were calculated and are shown below. a.Calculate the narrow-sense heritability for both traits (calcium and growth hormone levels).
b.Which trait, if any, will most likely respond to artificial selection?

Question 41

Which of the following statements about realized heritability is NOT correct?

A)Realized heritability can be estimated as a ratio between values of response to selection (R)and selection differential (S)(e.g., R/S).
B)Realized heritability can be estimated as a product of two values, response to selection (R)and selection differential (S)(e.g., R * S).
C)Response to selection (R)is influenced in part by narrow-sense heritability value.
D)Response to selection (R)is influenced in part by the magnitude of difference between the mean phenotype of selected parents and the mean phenotype of original population
E)Selection differential (S)can be estimated as a product between values of response to selection (R)and realized heritability (h²)(e.g., R * h²)

Question 42

The following components of the total phenotypic variance were estimated at three agriculturally important traits in corn. Determine which of these traits will have the BEST response to selective breeding.

A)Trait A
B)Trait B
C)Trait C
D)All traits will respond in a similar manner.
E)None of these traits will respond to selective breeding.

Question 43

The following broad-sense heritability values were estimated for the same trait in three populations: 0.3, 0.6, and 0.8 for populations A, B, and C, respectively.Which of these populations will likely respond better to (the same)selection experiments?

A)Population A
B)Population B
C)Population C
D)All of these populations will respond in a similar manner.
E)This cannot be determined from the information given.

Question 44

The following components of the total phenotypic variance were estimated at three agriculturally important traits in corn. Determine which of these traits has the LARGEST broad-sense heritability.

A)Trait A
B)Trait B
C)Trait C
D)All traits will have the same broad-sense heritability.
E)Traits B and C will have the same broad-sense heritability.

Question 45

Realized heritability experiments were conducted on three bristle-associated traits in fruit flies, with the following h² (realized heritability)and S (selection differential)values estimated.Which of these traits has the LOWEST response to selection (R)value?

A)Trait A
B)Trait B
C)Trait C
D)Traits A and B have the same (i.e., low)response to selection values.
E)Traits B and C have the same (i.e., low)response to selection values.

Question 46

Which of the following statements about plant height heritability is CORRECT?

A)In plant height experiments, estimates of heritability under the same light/humidity conditions will be the same regardless of the genotypes of parents.
B)In plant height experiments, estimates of heritability under the same light conditions will be the same regardless of the humidity values.
C)Heritability values will become larger as the plants themselves get older.
D)Estimates of plant height heritability may vary under different growing conditions, including changes in light/humidity.
E)A difference in heritability between two plant populations indicates that genetic factors only influence plant height in one of the populations.

Question 47

Which of the following statements about heritability is NOT correct?

A)An individual does not have heritability.
B)Some individuals have higher heritability than others.
C)Heritability values may vary even for the same trait.
D)Environment may influence the trait even if heritability values are very high.
E)Traits with low heritability values are influenced by the environment to a larger extent than traits with high heritability values.

Question 48

The following broad-sense heritability values were estimated for four different traits: 0.2, 0.3, 0.4, and 0.5 for traits A, B, C, and D, respectively.Which of these traits experiences the LARGEST influence of the environment?

A)Trait A
B)Trait B
C)Trait C
D)Trait D
E)All of these traits are influenced by the environment in a similar manner.

Question 49

Which of the following traits is likely to have QTLs influencing that characteristic?

A)Blood pressure in humans
B)Height in humans
C)Muscle mass in humans
D)All of these traits are correct.
E)Only blood pressure and muscle mass in humans are correct.

Question 50

The following narrow-sense heritability values were estimated for the same trait in three populations: 0.3, 0.6, and 0.8 for populations A, B, and C, respectively.Which of these populations will likely respond better to (the same)selection experiments?

A)Population A
B)Population B
C)Population C
D)All of these populations will respond in a similar manner.
E)This cannot be determined from the information given.

Question 51

The following narrow-sense heritability values were estimated for four different traits: 0.2, 0.3, 0.4, and 0.5 for traits A, B, C, and D, respectively.Which of these traits has the LARGEST dominance genetic variance?

A)Traits A and B
B)Trait C
C)Trait D
D)All of these traits are influenced by the environment in a similar manner.
E)This cannot be determined from the information given.

Question 52

Realized heritability experiments were conducted on three bristle-associated traits in fruit flies, with the following R (response to selection)and S (selection differential)values estimated.Which of these traits has the HIGHEST narrow-sense heritability?

A)Trait A
B)Trait B
C)Trait C
D)Traits A and B have the same (i.e., high)narrow-sense heritability values.
E)Traits B and C have the same (i.e., high)narrow-sense heritability values.

Question 53

The following height measurements (in cm)were taken for two groups of students, depicted on the stem-and-leaf diagram.Which of the groups has the largest mean height?

A)Group 1
B)Group 2
C)Both groups have the exact same mean height.
D)It cannot be determined.

Question 54

Which of the following statements about realized heritability is CORRECT?

A)Realized heritability can be estimated as a ratio between values of genetic variance (V_G)and selection differential (S)(e.g., V_G /S).
B)Realized heritability can be estimated as a product of two values, response to selection (R)and selection differential (S)(e.g., R × S).
C)Selection differential (S)is directly correlated with the environmental variance V_E.
D)Response to selection (R)is influenced in part by the ratio between narrow-sense heritability (h²)and total phenotypic variance V_P.
E)Selection differential (S)can be estimated as a ratio between values of response to selection (R)and realized heritability (h²)(e.g., R/ h²).

Question 55

Narrow-sense heritability of height in humans was estimated at about 0.8.What does that tell us about the trait in a group of 100 students?

A)That 80 of students will be tall
B)That 20 of the students will be tall
C)That at least 20 of them will have medium-to-tall height variation
D)That 20% of variation of this trait can be attributed to additive genetic variance
E)That 80% of variation of this trait can be attributed to additive genetic variance

Question 56

Which of the following statements about heritability is CORRECT?

A)Individuals within a population all have the same heritability.
B)Some individual characteristics have higher heritability than others.
C)Heritability values remain constant over the life-span of an individual.
D)Environment plays a predominant role if heritability values are very high.
E)A difference in heritability between populations is indicative of a stronger influence of genetic factors in a population with a higher heritability.