Deck 5: Quantitative Genetics

Question 1

In parent-offspring regression, the average value of the parents is termed the

A) parental average.
B) modal parental value.
C) midparent value.
D) median parental value.
E) mean parental value.

Answer 1

C

Question 2

In maize, some alleles at the seed coat locus influence our ability to visually determine the endosperm color phenotype. Specifically, an opaque seed coat prevents us from seeing the endosperm within, while we can readily see the endosperm in seeds with transparent coats. The opaque coat color allele thus appears to mask the expression of endosperm color alleles, providing an example of

A) pleiotropy.
B) maternal effects.
C) polygenic inheritance.
D) codominance.
E) epistasis.

Answer 2

E

Question 3

A broad-sense heritability of 0.8 for a particular trait indicates that

A) genetic differences among individuals account for much of the phenotypic variation for that trait.
B) the trait is 80 percent heritable.
C) phenotypic variation stems from environmental influences.
D) genes and environment play equal roles in shaping the trait.
E) None of the above

Answer 3

A

Question 4

The proportion of phenotypic variance that results from additive genetic variance is the ________ heritability.

A) genetic
B) broad-sense
C) narrow-sense
D) generic
E) multifactorial

Question 5

Which of the following is a source of genetic variation in a population caused by epistatic interactions between genes?

A) Interaction variance
B) Dominance variance
C) Additive genetic variance
D) Maternal effects
E) General environmental effects

Question 6

The proportion of phenotypic variance in a population that results from genetic differences among individuals is expressed as the

A) narrow-sense heritability.
B) environmental variance.
C) broad-sense heritability.
D) additive genetic variance.
E) interaction variance.

Question 7

Genes that affect many phenotypes are

A) polymorphic.
B) pleiotropic.
C) multifactorial.
D) epistatic.
E) polygenic.

Question 8

Ornamental hydrangeas are well known to produce blue or magenta flowers, depending on soil pH. This may be a good example of a discrete trait influenced by

A) other genes.
B) environment.
C) genetics.
D) A and B.
E) A, B, and C.

Question 9

When graphing a distribution of phenotypes for a continuous trait, a broad curve implies

A) a large standard deviation.
B) zero regression line slope.
C) a large correlation coefficient.
D) little variation in the phenotypes.
E) a small variance.

Question 10

Which of the following is the main problem stemming from inadequately small sample sizes in statistics?

A) Sampling error
B) The sample is not representative of the population.
C) The sample may not be random.
D) The sample may be a biased subset of data points.
E) All of the above are true.

Question 11

In Emerson and East's maize studies, the range of phenotypic variation in the F2 population was ________ than that of the F1 population, as would be expected under the polygene hypothesis.

A) the same as
B) smaller
C) greater
D) random compared with
E) None of the above

Question 12

________ is used to measure how much a change in one variable is associated with a given change in another variable, while ________ is used to measure the strength of association between two traits.

A) Regression, correlation
B) ANOVA, correlation
C) Variance, covariance
D) Variance, heritability
E) Broad-sense heritability, narrow-sense heritability

Question 13

A Mendelian cross for a three-gene trait is expected to yield ________ F2 genotypes.

A) 4
B) 16
C) 27
D) 64
E) 265

Question 14

A quantitative trait influenced by four loci, each with two alleles, would be expected to show ________ possible genotypes.

A) 16
B) 8
C) 81
D) 256
E) None of the above

Question 15

In the general regression equation y = mx + b, variables m and b are ________ and ________, respectively.

A) x-intercept, y-intercept
B) regression line slope, y-intercept
C) narrow-sense heritability, broad-sense heritability
D) y-intercept, x-intercept
E) y-intercept, regression line slope

Question 16

A ________ trait is typically influenced by one or two genes.

A) continuous
B) polygenic
C) quantitative
D) discrete
E) multifactorial

Question 17

The distribution of continuous traits can best be described as

A) logarithmic.
B) linear.
C) hyperbolic.
D) bimodal.
E) bell-shaped.

Question 18

Multiple elements of the genome (chromosomal regions) linked through genetic analysis with specific phenotypic traits are also known as

A) continuous traits.
B) discontinous traits.
C) multifactorial traits.
D) quantitative trait loci.
E) polygenic loci.

Question 19

Populations of the snail Cepaea nemoralis exhibit three color morphs, a good example of a ________ trait.

A) continuous
B) quantitative
C) discontinuous
D) polygenic
E) B, C, and D

Question 20

Heritability can only be measured for

A) traits with genotypic but not phenotypic variance.
B) traits with phenotypic variance.
C) discrete traits.
D) polygenic traits.
E) none of the above.

Question 21

Continuous traits are often influenced by multiple simple (Mendelian) genes.

Question 22

Phenotypic traits of members of the same family have high heritability.

Question 23

Broad-sense heritability of a trait is estimated at 0.8. If the total phenotypic variance is estimated at 32.20, what is the genetic variance?

Question 24

In Mendel's day, "particulate" inheritance would have made less sense to people than blending inheritance. Why so?

Question 25

A botanist studying a plant with geographically disjunct and morphologically distinct populations wanted to know the degree to which the differences between the populations was attributable to genetic factors. Outline a simple experiment she can do to address this question.

Question 26

Distinguish between polygenic and multifactorial traits.

Question 27

Epistasis refers to the phenomenon where a given gene influences the expression of one or more other genes.

Question 28

The correlation coefficient is a measure of the strength of association between two traits. Correlation does not mean causation, however. Think of one or two variables (not necessarily phenotypes) that are correlated and are causally linked, and one or two variables that may be correlated but are not likely to be causally linked.

Question 29

The mean value of a quantitative trait in F1 offspring is generally smaller than either of the values of the parentals.

Question 30

Narrow-sense heritability is a more useful measure than broad-sense heritability in agricultural selective breeding.

Question 31

A regression analysis of two traits yielded a slope of 0. Explain the biological meaning of this value.

Question 32

Explain why narrow-sense heritability is a more accurate indicator of responsiveness to selection than is broad-sense heritability.

Question 33

Continuously varying traits typically show a bell-shaped frequency distribution. Explain why this is so; why are intermediate phenotypes more frequent than phenotypes at either end of the distribution?

Question 34

Define, in your own words, the biological meaning of heritability.

Question 35

Narrow-sense heritability for a trait can be obtained from a regression of midparent value on offspring value.

Question 36

If you measured narrow-sense heritability of a crop plant trait at 0.25, what would that value mean in terms of the ease of selecting the trait in a selective breeding program?

Question 37

As the number of genes influencing a quantitative trait increases, the range of phenotypic variation is expected to increase.

Question 38

Evolution is defined as genetic change in populations over time.

Question 39

A gene that influences several traits is termed pleiotropic.

Question 40

Human fingerprints are a good example of a multifactorial trait. What evidence can you cite to suggest that fingerprints are partially influenced by genes? How about evidence suggesting that they are partially influenced by environmental factors?

Question 41

Breeders seeking to change a phenotypic trait require, ideally, a strong genetic component to the trait. It is most desirable, however, that this genetic component comes from additive genes and not genes with dominance or interaction variance. Why?

Question 42

Identical (monozygotic) and fraternal (dizygotic) twins provide a natural experiment for investigating the influence of genetics on traits. Outline a study approach using twins, assuming you could identify enough pairs, in which you are examining the relative contribution of genetics on blood cholesterol level.

Question 43

The average adult height in the U.S. population has increased by several centimeters over the past two generations. Is this likely to reflect a change in the genetic makeup of the population, a change in environmental factors, or both? Explain.