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23
The Mechanisms of Evolution
TEST FILE QUESTIONS
Fill in the Blank
1. _______________ is the accumulation of heritable changes within populations over
time.
Answer: Evolution
2. The frequencies of the variants at each locus in a population are called _______.
Answer: allele frequencies
3. The genetic expression of traits (e.g., “homozygous recessive”) is called the
organism’s _______.
Answer: genotype
4. The physical expression of a trait (e.g., height or eye color) describes an organism’s
_______.
Answer: phenotype
6. The _______ is the sum total of genetic information in a population at any given
moment. It includes every allele at every locus in every organism.
Answer: gene pool
9. A population that is not changing (i.e., it has constant genotype and allele frequencies
Answer: equilibrium
10. _______ involves movement of individuals to a new location, followed by breeding.
Answer: Gene flow
11. The differential contribution of offspring resulting from different heritable traits is
called _______.
Answer: natural selection
12. The idea of natural selection is most closely associated with _______, who proposed
it in 1859 in his book The Origin of Species.
Answer: Charles Darwin
14. Genetic drift can be brought about either by a severe reduction in population size,
known as a population _______, or by a small number of individuals’ establishing a new
population, which results in a _______.
Answer: bottleneck; founder effect
16. A _______ is a change in DNA sequence.
Answer: mutation
Multiple Choice
1. Assume that a population is in Hardy–Weinberg equilibrium for a trait controlled by
one locus and two alleles. If the frequency of the recessive allele is 0.90, what is the
frequency of the dominant allele?
a. 0.10
b. 0.19
c. 0.81
d. None of the above
e. This cannot be answered without more information.
Answer: a
2. There is a gene that causes people to have crumbly earwax. This gene is expressed as a
complete dominant: Individuals who are homozygous dominants (CC) or heterozygous
(Cc) have crumbly earwax. Homozygous recessives (cc) have gooey earwax. On Paradise
Island there are 100 people, 75 of whom have crumbly earwax. Assuming Hardy–
Weinberg conditions, what is the frequency of the c allele on Paradise Island?
a. 0.25
b. 0.50
c. 0.87
d. None of the above
e. This cannot be answered without more information.
Answer: b
3. In a population at Hardy–Weinberg equilibrium, the frequency of heterozygotes is
0.64. What is the frequency of the homozygous dominants?
a. 0.08
b. 0.64
c. 0.80
d. None of the above
e. This cannot be answered without more information.
Answer: e
4. In a population at Hardy–Weinberg equilibrium, the frequency of the a allele is 0.60.
What is the frequency of individuals heterozygous for the A gene?
a. 0.16
b. 0.24
c. 0.48
d. None of the above
e. This cannot be answered without more information.
Answer: c
5. There are five conditions that must be met for a population to be in Hardy–Weinberg
equilibrium. Which of the following is not one of those conditions?
a. Nonrandom mating
b. Large population size
c. No migration
d. No natural selection
e. No mutations
Answer: a
6. Which of the following populations would demonstrate a population bottleneck?
a. The population of El Paso, Texas, after it has moved in its entirety to Patagonia
b. Eight male and eight female elephant seals that have survived the wreck of the Exxon
Valdez
c. A million male orangutans
d. Six male orangutans collected from a natural population in Sumatra and moved to the
San Diego Zoo
e. None of the above
Answer: b
7. _______ is the effect produced when a bee carries pollen from one population to
another.
a. Gene flow
b. A population bottleneck
c. A founder event
d. Genetic equilibrium
e. Assortative mating
Answer: a
11. _______ selection occurs when the extremes of a population contribute relatively few
offspring to the next generation as compared to average members of the
a. Corrective
b. Directional
c. Stabilizing
d. Disruptive
e. Natural
Answer: c
12. _______ selection occurs when one extreme of a population contributes more
offspring to the next generation than average members of the population do.
a. Corrective
b. Directional
c. Stabilizing
d. Disruptive
e. Natural
Answer: b
13. Which of the following agents of evolution adapts a population to its environment?
a. Nonrandom mating
b. Natural selection
c. Migration
d. Genetic drift
e. Mutation
Answer: b
14. The raw material for evolutionary change is _______ variation.
a. phenotypic
b. genetic
c. geographical
d. environmentally-induced
e. behavioral
Answer: b
15. A population evolves when
a. environmentally-induced variation is constant between generations.
b. individuals with different genotypes survive or reproduce at different rates.
c. the environment changes on a seasonal basis.
d. members reproduce by cloning.
e. juvenile and adult stages require different environments.
Answer: b
24. A gene pool consists of all the alleles
a. of an individual’s genotype.
b. present in a specific population.
c. that occur in a species throughout its evolutionary existence.
d. that contribute to the next generation of a population.
e. of a biome.
Answer: b
33. In the Hardy–Weinberg equation, the homozygous dominant individuals in a
population are represented by
a. p2.
b. 2pq.
c. q2.
d. p.
e. q.
Answer: a
38. A mutation occurs in one of your lung cells. Which of the following is true?
a. You have evolved to be better adapted to your environment.
b. You will soon die because most mutations are lethal.
c. You will be sterile and no longer be able to have children.
d. The human species will have evolved because this mutation will be passed on to your
children.
e. This mutation does not affect human evolution because it will not be passed on to your
offspring.
Answer: e
44–46. In a population of 200 individuals, 72 are homozygous recessive for the character
of eye color (cc). One hundred individuals from this population die due to a fatal disease.
Thirty-six of the survivors are homozygous recessive. Answer the following questions.
44. In the original population, the frequency of the dominant allele is
a. 0.16.
b. 0.36.
c. 0.40.
d. 0.48.
e. 0.60.
Answer: c
45. In the new population, the frequency of the dominant allele is
a. 0.16.
b. 0.36.
c. 0.40.
d. 0.48.
e. 0.60.
Answer: c
46. How many heterozygous individuals are expected in the new population?
a. 16
b. 36
c. 40
d. 48
e. 60
Answer: d
47. Which of the following is not an effect of sexual recombination on alleles?
a. Greater evolutionary potential
b. Change in the frequency of specific alleles
c. Greater genotypic variety
d. New combinations of genetic material
e. Greater phenotypic variety
Answer: b
48. An allele that does not affect the fitness of an organism is called a _______ allele.
a. neutral
b. directional
c. distributed
d. positive
e. natural
Answer: a
Problems:
Based on lab problems
1. The allele for spherical seeds in pea plants is dominat to that for wrinkled seeds. In a
population of 4000 pea plants 500 show the recessive phenotype. What is the frequency
of the homozygous dominant and heterozygous genotypes within the population?
2. In a population of 1,000 individuals, the dominant phenotype of a trait occurs 55% of
the time. What is the frequency of the dominant and recessive alleles?
3. A lethal recessive condition is responsible for the death of 1 out of every 20,000
babies born in South America.
a. What is the frequency of homozygous recessive individuals in the population?
q2 = 1/20,000 = 0.00005
b. What is the frequency of the recessive allele in the population?
q = sqrt 0.00005 = 0.007