Deck 22: Quantitative Genetics

Question 1

Analysis of specific genetic contributions to quantitative traits has been done by

A)altering the environment of individuals and observing phenotype alterations.
B)completing sequencing of specific genes for various species.
C)measuring V_G by adding V_A,V_D,and V_I.
D)conducting ANOVA on genetic markers and phenotypes to identify linkage to QTLs.
E)measuring specific environmental effects,such as sunlight,on phenotype.

Answer 1

D

Question 2

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

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

Answer 2

B

Question 3

The distribution of continuous traits can best be described as

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

Answer 3

B

Question 4

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

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

Question 5

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

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

Question 6

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

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

Question 7

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 8

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

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

Question 9

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

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

Question 10

A female cat that is small due to nutritional deficiencies experienced in early life will give birth to smaller kittens than a genetically identical cat that is larger in size due to better nutrition in early life,even if both female cats were bred to the same male cat and both had good nutrition during pregnancy.The term that is used in measuring this type of variation is

A)V_P.
B)V_E.
C)V_EG.
D)V_ES.
E)V_EM.

Question 11

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

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

Question 12

Quantitative traits typically have multiple genetic influences in which alleles of a number of genes contribute individual amounts to the final phenotype without classical dominance or epistasis.The term used for the observed variation that results from this is

A)V_A.
B)V_D.
C)V_E.
D)V_G.
E)V_I.

Question 13

Which of the following statements about heritability is true?

A)Broad-sense heritability defines the complete genetic basis of a trait.
B)Heritability is fixed for a given trait.
C)Traits shared by members of the same family do not necessarily have high heritability.
D)Heritability is the measure of the proportion of an individual's phenotype that is due to genetics.
E)If a population displays little variation in a given trait,then that trait has low heritability

Question 14

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

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

Question 15

Which of the following problems might arise in a statistical study as a result of a population sample of inadequate size?

A)A non-representative sample
B)Sampling error
C)A non-random sample
D)A sample drawn from a biased subset of data points
E)All of these

Question 16

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

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

Question 17

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

Question 18

Heritability can only be measured for

A)traits with phenotypic variance.
B)traits with genotypic variance.
C)discrete traits.
D)polygenic traits.
E)None of these

Question 19

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

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

Question 20

If you measured the 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 21

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 22

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

Question 23

A botanist studying a plant with geographically separated and morphologically distinct populations wants to know the degree to which the differences between the populations are attributable to genetic factors.Outline a simple experiment she can perform to address this question.

Question 24

In descriptive statistics,the median is defined as the value exactly in the center of a distribution,with half the values lying above and half lying below.

Question 25

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

Question 26

The 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 27

Evolution is defined as genetic change in populations over time.

Question 28

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

Question 29

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

Question 30

If a populations shows very little phenotypic variance for a trait,then that trait is probably controlled principally by the environment rather than genetics.

Question 31

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

Question 32

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

Question 33

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

Question 34

If members of the same family display the same phenotypic traits,these traits have high heritability.

Question 35

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

Question 36

The correlation coefficient is a measure of the strength of association between two traits.Correlation,however,does not indicate causation.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 37

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

Question 38

A gene that influences several traits is termed pleiotropic.

Question 39

Distinguish between polygenic and multifactorial traits.

Question 40

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 41

In a controlled cross for a quantitative trait,600 F₂ offspring are obtained,10 of which exhibit the phenotype of one of the parentals.How many genes are estimated to control this trait based on these results?

Question 42

An isolated population of wild turkeys has adult males that weigh an average of 18 pounds and females that weigh an average of 10 pounds.Another isolated population living 100 miles north has a population where adult males weigh 13 pounds and females 8 pounds on average.Both populations have a very low phenotypic variance.How could you determine genetic contributions to the weight differences between the populations?

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.

Question 44

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