Question 1

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

Accepted Answer

Narrow-sense heritability is defined in terms of additive genetic variance, meaning that each allele of each contributing gene has a phenotypic effect. Broad-sense heritability is based on genetic variance in general. Since selective breeding is based on phenotypes, insofar as additive genetic variance is a more precise reflection of genotype underlying phenotype, this measure will help make better selective-breeding decisions.

Question 2

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

Accepted Answer

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

Question 3

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.

Accepted Answer

If there is a genetic predisposition to achieving a certain blood cholesterol level, monozygotic twins might be expected to show a stronger statistical association in cholesterol level than dizygotic twins. You would need to control for environment, however: ideally, your twins should be exposed to different diets for a specified period.

Question 4

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?

Accepted Answer

The greater the genetic contribution fro

Question 5

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

Accepted Answer

A) True 
 B)False

Question 6

A gene that influences several traits is termed pleiotropic.

Accepted Answer

A) True 
 B)False

Question 7

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

Accepted Answer

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

Question 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

Phenotypic variation

Question 10

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?

Accepted Answer

VG = 25.76

Question 11

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

Accepted Answer

Heritability is often imprecisely define

Question 12

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?

Accepted Answer

The greater frequency of intermediate ph

Question 13

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

Accepted Answer

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

Question 14

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.

Accepted Answer

Traits like possession of a Y chromosome

Question 15

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

Accepted Answer

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

Question 16

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.

Accepted Answer

Two classic experimental approaches are

Question 17

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

Accepted Answer

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

Question 18

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

Accepted Answer

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

Question 19

________ 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.

Accepted Answer

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

Question 20

Evolution is defined as genetic change in populations over time.

Accepted Answer

A) True 
 B)False

Exam 5: Quantitative Genetics

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

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

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?

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

A gene that influences several traits is termed pleiotropic.

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

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

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

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?

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

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?

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 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.

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

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

________ 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.

Evolution is defined as genetic change in populations over time.

Genetics of Bacteria and Bacteriophages

Variations in Chromosome Structure and Number

Advanced Gene Mapping in Eukaryotes

Gene Mapping in Eukaryotes

Extensions of Mendelian Genetic Principles

Chromosomal Basis of Inheritance

Molecular Evolution

Population Genetics

Non-Mendelian Inheritance

Genetics of Cancer

Genetic Analysis of Development

Regulation of Gene Expression in Eukaryotes

Mendelian Genetics

Regulation of Gene Expression in Bacteria and Bacteriophages

Genomics

Applications of Recombinant DNA Technology

Recombinant DNA Technology

DNA Mutation, DNA Repair, and Transposable Elements

Gene Expression: Translation

Gene Expression: Transcription

Gene Control of Proteins

DNA Replication

DNA: The Genetic Material

Genetics: an Introduction

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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.