Chapter 6 Quiz

. Which example does not include a case of phenotypic variance?

A population of humans in which individuals differ in height

A genetically uniform population of barnacles express more muscular reproductive organs in wavy environments

A population of bacteria is polymorphic for a single nucleotide polymorphism that resulted from a synonymous mutation

A population of garter snakes with several color patterns use different escape behaviors

A population of finches has their bill size increased by directional selection

. Refer to the figure showing the fitness function for combinations of two traits in the northwestern garter snake (Thamnophis ordinoides), based on survival in the field.

If we ignore the long-term effects of genetic drift, what effect will correlational selection have on coloration and escape behavior by this garter snake population?

Linkage disequilibrium in the population, where some combinations of genotypes and phenotypes are much more common than others

Extinction of striped individuals that reverse course when fleeing predators.

Coexistence of each of the four possible phenotype combinations.

Mixtures of each phenotype produced by genetic recombination.

Learning by the garter snakes' predators, changing the fitness landscape.

. Which of the following would likely cause the greatest mean rates of change to morphological characters in a large population with a constant mutation rate?

Genetic drift

Directional selection

Fluctuating selection

Stabilizing selection

A condition of stasis

. Imagine a population of Galápagos finches that vary for bill size. If the population mean is near the optimum size for eating the seeds found on the island, what would we expect to occur if their main seed resource goes extinct, and another plant with much larger seeds replaces it?

Stabilizing selection maintaining the population average

Disruptive selection increasing phenotypic variance for bill size

Correlational selection between seed size and bill size

Directional selection increasing bill size towards a new optimum

Extinction of the new plant as finches each all its seeds

. Refer to the graph showing the pattern of newborn human survival as a function of birthweight.

Based on the graph and what you know about modes of selection, estimate the selection gradient, β, on birthweight.

A high, positive value

A low, positive value

A value very near zero

A low negative value

A high, negative value

. What happens to the heritability of a trait as the most fit allele in the population approaches fixation?

The heritability is equal to the selection gradient for that locus.

Heritability increases as natural selection is relaxed.

Heritability remains constant because all traits are still coded by genes passed from parent to offspring.

Heritability drops towards zero because phenotypic variation is only contributed by environmental variance.

Heritability increases towards 1, following the frequency of the allele.

. The change in the average trait value of a population under selection is equal to the heritability multiplied by the selection differential. The selection differential is the

difference in average number of offspring produced by each phenotype.

difference in population trait mean before and after selection.

difference in relative fitness between members of the population with different genotype.

percent change in likelihood of survival and reproduction.

variance in the measurements of the trait in the population.

. Phenotypic variance that is not due to genetic variance can be attributed to

environmental variance.

dominance.

epistasis.

pleiotropy.

linkage disequilibrium.

. Response of a quantitative character to selection will be greatest when heritability is _______ and selection is _______.

0.40; 2.5

0.40; 4

0.60; 4

0.75; 2.5

0.75; 4

. Which condition might interfere with a breeder's attempt to predict the change in a trait over many generations based on their knowledge of the trait's heritability?

Linkage disequilibrium

New genetic mutations

A change in genetic variance

Natural selection

All of the above

. The phenotypic effect of synergistic interactions among loci is referred to as

heritability.

dominance.

epistasis.

pleiotropy.

linkage disequilibrium.

. Many people think long-term evolution of a species must follow the rule "adapt or die." Which of the following will not help organisms overcome an environmental change that threatens extinction?

The will to survive

High levels of genetic variation

A large population size

Phenotypic plasticity that buffers environmental change

A high rate of beneficial mutations

. Stabilizing selection is often observed in nature because of

selection on variance.

trade-offs.

linkage disequilibrium.

variable selection.

realized heritability.

. What is meant by the statement "Evolution may proceed along 'genetic lines of least resistance'"?

Because mutations may be more likely to appear at some locations in a gene than at others, we can easily predict the phenotype it will experience when natural selection occurs.

Evolution operates on the set of phenotypes that a genotype can produce under all possible environmental conditions.

Functionally correlated characters will not remain genetically correlated, because they are broken up during segregation and crossing over.

Characters with little genetic variation will constrain the rate of natural selection; correlated characters may increase in fitness less rapidly, because they can evolve only along the greatest axis of variation.

The phenotypes produced by genes under selection will be those that require the least energy input, despite potential fitness gains.

. Anthropogenic climate change is taking place at such a fast rate that many species will fail to adapt quickly enough to avoid extinction. Which of the following may constrain evolution in response to human-induced climate change?

Lack of heritable genetic variation for relevant traits

Genetic correlations between relevant traits and other traits that conflict with the direction of selection

Loss of genetic variation in relevant traits by genetic drift in dwindling populations

Lack of new mutations that allow adaptation to new climate conditions

All of the above

. Genetic correlations can have two causes: _______ and _______.

linkage disequilibrium; pleiotropy

linkage disequilibrium; epistasis

epistasis; pleiotropy

phenotypic correlation; environmental correlation

phenotypic correlation; pleiotropy

. In correlated selection, selection favors some combination of character states over others, usually because the characters

are on different chromosomes.

are functionally related.

are phenotypically plastic.

are canalized.

represent a trade-off.

. Which pair of traits are least likely to be genetically correlated?

Two traits that are affected pleiotropically by a single locus

Two morphological traits that must "fit" or "work" together

A morphological trait that works best with a specific behavioral trait

Two traits that are in linkage disequilibrium with each other

Two traits whose appearance varies based on the environmental conditions

. When the environment affects the phenotypes of all the genotypes in a population and the reaction norms of the genotypes are parallel,

phenotypic variance includes environmental variance, genetic variance, and a genotype by environment interaction.

only genetic variance and environmental variation contribute to phenotypic variance.

phenotypic variation is driven by genetic variance only.

phenotypic variation is driven by environmental variance only.

phenotypic variation is driven by a genotype by environment interaction only.

. QTL mapping is a method for detecting loci that contribute to quantitative trait variation. This method relies on the association between phenotypic differences and molecular markers. A QTL typically refers to a

morphological mutation.

molecular mutation.

quantitative trait.

chromosome region that may include many genes.

single gene.

Chapter 6 Quiz

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