Biology (Raven), 10th Edition

Chapter 20: Genes Within Populations

Post-Test

1
A few individuals of a new yellow morph of a species of water boatman (an insect preyed upon by some fish) are introduced into a population. Its frequency increases rapidly and then settles at about 50%. This is an example of:
A)directional selection.
B)Negative frequency-dependent selection.
C)a balance between drift and selection.
D)positive frequency-dependent selection.
E)none of the above adequately explain this phenomenon.
2
It is observed in a population that the frequency of intermediate types is favored. This is likely the result of:
A)directional selection.
B)chance.
C)stabilizing selection.
D)disruptive selection.
E)none of the above
3
It is found that artificial selection to increase beak length in chickens also reduces skull thickness. This is an example of:
A)bad luck.
B)stabilizing selection.
C)pleiotropy.
D)epistasis.
E)linked genes
4
For a trait to evolve by natural selection there must be
A)variation among individuals.
B)a mechanism of inheritance.
C)fitness differences among individuals based on that trait.
D)variation among individuals and a mechanism of inheritance.
E)All of these choices are correct.
5
The Hardy-Weinberg principle states that the genotypes in the next generation will be in the proportions p2:2pq:q2 (where p and q are the frequencies of two alleles in the population) after one generation of
A)mutation.
B)assortative mating.
C)random mating.
D)selection.
E)inbreeding.
6
Genetic drift:
A)occurs in all populations.
B)has the greatest effect in small populations.
C)can reduce genetic variation in a population.
D)can lead to loss of alleles in isolated populations.
E)All of the above.
7
True or False: An organism's fitness depends only on its survival:
A)True
B)False
8
A cline is a gradual change in the frequency of a trait over a geographical distance. For example a melanic form of an insect may replace the non-melanic form over a distance of several hundred kilometres. This is an example of the balance between:
A)mutation and drift.
B)drift and selection.
C)drift and gene flow.
D)mutation and gene flow.
E)selection and gene flow.
9
The disease sickle-cell anemia is maintained at relatively high frequencies in populations in Africa and Asia by:
A)heterozygote advantage.
B)a balance between mutation and selection.
C)a balance between drift and selection.
D)a balance between mutation and drift.
E)disruptive selection.
10
Disruptive selection favors:
A)intermediate phenotypes.
B)phenotypes only at one end of the range.
C)no phenotypes.
D)phenotypes at both ends of the range.
E)none of the above
11
Experimental studies of natural selection have shown that:
A)selection occurs very slowly in natural populations as a rule.
B)it is impossible to demonstrate that selection occurs at all.
C)selection can occur very rapidly.
D)other evolutionary factors are more important.
E)while selection is a possible force in evolution, genetic drift is far more important in the evolutionary change of species.
12
Increase (or decrease) in a trait by selection may not occur if:
A)there is no genetic variation in the population for the trait.
B)genes determining the trait have pleiotropic effects.
C)genes determining the trait interact with other genes.
D)the rate of gene flow among populations is high.
E)all of the above
13
In a population of 100 students, 64 were PTC tasters with genotype TT, 32 were PTC tasters with genotype Tt and the last 4 were non-tasters with genotype tt. What is the allelic frequency t?
A)0.8
B)0.4
C)0.6
D)0.5
E)0.2
14
In a population of 100 fish, 64 are dull colored with genotype CC, 32 were dull colored with genotype Cc and the last 4 were brightly colored with genotype cc. What is the genotypic frequency of cc?
A)0.4
B)0.6
C)0.5
D)0.8
E)0.2
15
Population geneticists have developed mathematical formulas that predict how gene pools will change in response to fluctuations in size, geographic location, or genetic composition. The most recognized of these is the
A)Hardy-Weinberg equation
B)Stabilizing selection formula
C)Fitness equation
D)Darwin formula
E)Mutation rate equation
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