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Flashcards in Chapter 6 Deck (16)
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1
Q

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?

A

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

2
Q

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?

A

Directional selection

3
Q

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

A

0.75; 4

4
Q

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

A

Difference in population trait mean before and after selection

5
Q

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?

A

Natural selection
Linkage disequilibrium
A change in genetic variance
New genetic mutations

6
Q

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

A

Epistasis

7
Q

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?

A

Lack of new mutations that allow adaptation to new climate conditions
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

8
Q

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

A

Two traits whose appearance varies based on the environmental conditions

9
Q

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

A

Environmental variance

10
Q

Why do quantitative traits show continuous variation?

A

Quantitative traits depend on both genetic and environmental factors. The phenotypic traits in which are quantitative traits are termed “discrete phenotypes.” These traits are continuous in the sense that the expression falls within a numerical characterization spectrum. Example of such traits are height, blood pressure, and crop yield. Phenotypic evolution is primarily based on allele frequency changes at multiple loci thereby instigating more phenotypic variation with the existing allele population and without new genotypic variation. With the additional influence of the environment variable, quantitative traits show further continuous variation.

11
Q

Natural selection and genetic drift are the two most important causes of evolutionary change. How do they differ?

A

Genetic drift is nonadaptive; it changes allele frequency without regard to fitness

12
Q

A large population of three-spined stickleback fish lives in an Alaskan lake. Two alleles segregate at a neutral locus. The allele frequency of the first allele is 0.78. What is the most likely frequency of that allele in the next generation?

A

0.79

13
Q

Which condition is most likely to account for a difference between the census population size (total number of individuals) and the effective population size (Ne) in a rapidly growing population of humans?

A

Individuals take long time to reach sexual maturity

14
Q

Which observation would be the best evidence for a recent founder event or population bottleneck?

A

Low genetic diversity in a single population of a widely distributed species

15
Q

In the late eighteenth century, a typhoon swept through the Pacific atoll of Pingelap, leaving approximately 20 survivors. A large percentage of the present-day inhabitants of Pingelap are color blind. One can conclude, therefore, that the population experienced a

A

Bottleneck

16
Q

In Chapter 6 you saw how quantitative traits evolve in response to selection. Quantitative traits can also evolve by random genetic drift. Discuss how you expect the population size might affect the additive genetic variance within a population and the divergence between populations for a quantitative trait.

A

Linkage disequilibrium may be the result of genetic drift and could potentially influence quantitative traits. Population size based on genetic drift impacts the additive genetic variance within a population through the allowance for directional selection to occur simultaneously decreasing additive genetic variance particularly in smaller populations. Consequently, there would be increased genetic variance between populations of any size in the divergence. However, genetic drift is unlikely to produce a strong correlation between phenotype and its coexisting environment, the two underlying factors in quantitative traits, and therefore does not have a large influence in the phenotypic evolution of quantitative traits.