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17 Evolution of Populations
Chapter Test
Multiple Choices
Circle the best answers of the question .
_____ 1. Natural selection acts directly on
a. alleles.
c. phenotypes.
b. genes.
d. mutations.
_____ 2. In organisms that reproduce sexually, most variation that can be inherited is due to
a. mutations during gamete formation
b. polygenic traits
c. gene recombination during sexual reproduction
d. the effects of radiation.
_____ 3. The number of phenotypes produced for a given trait depends upon
a. the number of genes that control the trait.
b. which form of the trait is dominant.
c. the allele frequencies of the various alleles.
d. the relationship of allele frequencies to Mendelian ratios.
_____ 4. One end of Figure 17–1 shows an increase in
average beak size for a population of birds.
When individuals at only one end of a bell
curve of phenotype frequencies have high
fitness, the result is
a. directional selection.
b. stabilizing selection.
c. disruptive selection.
d. genetic drift.
Figure 17–1
_____ 5. Figure 17–2 shows highest fitness toward the
center of the curve. When individuals with an
average form of a trait have the highest
fitness, the result is
a. not predictable.
b. disruptive selection.
c. directional selection
d. stabilizing selection.
Figure 17–2
_____ 6. If a mutation introduces a new skin color in a lizard population, which factor might determine whether the
frequency of the new allele will increase?
a. how many other alleles are present
b. whether the mutation makes some lizards more fit for their environment than other lizards
c. how many phenotypes the population has
d. whether the mutation was caused by nature or by human intervention
_____ 7. Which of the following events do biologists consider a random change?
a. directional selection
c. disruptive selection
b. speciation
d. genetic drift
_____ 8. The situation in which allele frequencies in the gene pool of a population remain constant is called
a. evolution.
c. genetic equilibrium.
b. genetic drift.
d. natural selection.
_____ 9. The allele frequencies of a population are more likely to change if
a. the population size is increased.
b. no immigration or emigration occurs.
c. mating is not random.
d. the mutation rate decreases.
______10.Individuals at the upper and lower ends of the curve have higher fitness than individuals
a. not predictable.
b. disruptive selection.
c. directional selection
d. stabilizing selection.
near the