Lecture 8 / Chapter 26 - Population and Evolutionary Genetics

Question 1

Which of the following statements describes the members of a population?

• They all have the same genotype.
• They must be able to interbreed with one another.
• They must have the same allele for at least one genetic locus.
• They can include all of the plants and animals within a geographic area.

Answer 1

They must be able to interbreed with one another.

Members of a population must be able to interbreed, actually or potentially.

Question 2

What term is given to the total genetic information carried by all members of a population?

• gene pool
• genome
• breeding unit
• race
• chromosome complement

Answer 2

Gene pool.

Question 3

A number of mechanisms operate to maintain genetic diversity in a population. Why is such diversity favored?

• Genetic diversity helps populations avoid diploidy.
• Genetic diversity may better adapt a population to inevitable changes in the environment.
• Greater genetic diversity increases the chances of haploidy.
• Diversity leads to inbreeding advantages.
• Homozygosity is an evolutionary advantage.

Answer 3

Genetic diversity may better adapt a population to inevitable changes in the environment.

Question 4

A number of mechanisms operate to maintain genetic diversity in a population. Why is such diversity favored?

• Genetic diversity helps populations avoid diploidy.
• Genetic diversity may better adapt a population to inevitable changes in the environment.
• Greater genetic diversity increases the chances of haploidy.
• Diversity leads to inbreeding advantages.
• Homozygosity is an evolutionary advantage.

Answer 4

Genetic diversity may better adapt a population to inevitable changes in the environment.

Question 5

True or False?

If the frequency of the M allele in the human MN blood group system is 0.65 in a population at equilibrium, then the frequency of the N allele must be 0.04.

Answer 5

False.

The sum of the allele frequencies must equal 1, so the frequency of the N allele must be 0.35.

Question 6

If a recessive disease is found in 50 out of 100,000 individuals, what is the frequency of the heterozygote carriers for this disease?

• 0.956
• 0.0005
• 0.043
• 0.022

Answer 6

0.043

(If q 2 = 0.0005, then q = 0.022 and p = 1 − q = 0.978. The heterozygote frequency is 2pq, or 2 (0.978) (0.022) = 0.043.)

Question 7

In a population of birds in Africa, it was observed that birds with small or large beaks could efficiently crack and eat small or large seeds, respectively. Birds with intermediate beaks had trouble with both types of seeds. What type of selection would be expected to occur in this population if small and large seeds were the only types of food available to these birds?

• Disruptive
• Stabilizing
• Directional
• There would be no selection in this population.

Answer 7

Disruptive.

(Birds with an intermediate beak phenotype are at a disadvantage in this population and will be selected against because they are less fit.)

Question 8

In a population of 100 individuals, 49% are of the NN blood type. What percentage is expected to be MN assuming HardyWeinberg equilibrium conditions?

• 9%
• 42%
• 51%
• 21%
• There is insufficient information to answer this question.

Answer 8

42%

Question 9

Albinism is an autosomal recessive trait in humans. Assume that there are 100 albinos (aa) in a population of 1 million. How many individuals would be expected to be homozygous normal (AA) under equilibrium conditions?

• 100
• 10,000
• 19,800
• 980,100
• 999,999

Answer 9

980,100

Question 10

In a population that meets the Hardy-Weinberg equilibrium assumptions, 81% of the individuals are homozygous for a recessive allele. What percentage of the individuals would be expected to be heterozygous for this locus in the next generation?

Answer 10

18%

Question 11

Assume that in a Hardy-Weinberg population, 9% of the individuals are of the homozygous recessive phenotype. What percentage are homozygous dominant?

Answer 11

49%

Question 12

Assuming that p = 0.3 for a population in Hardy-Weinberg equilibrium, what would be the expected frequency of heterozygotes for the involved allelic pair?

Answer 12

0.42

Question 13

True or False?

If a gene has three alleles in a population, their frequencies must add up to 1.5.

Answer 13

False.

Question 14

Mutation and migration introduce new alleles into populations. What is the most likely principal force that will shift allelic frequencies within large populations?

Answer 14

Natural selection.

Question 15

The difference between fitness of a given genotype and another genotype considered optimal is called the selection coefficient (s). What is the selection coefficient for a genotype (aa) that produces an average of 99 offspring when Aa individuals produce an average of 100 offspring?

Answer 15

s = 0.01

Question 16

True or False?

In directional selection, both phenotypic extremes are equally selected against.

Answer 16

False.

Question 17

True or False?

Natural selection occurs when there is nonrandom elimination of genotypes from a population due to differences in viability or reproductive success.

Answer 17

True.

Question 18

Which of the following statements about mutations in population genetics is TRUE?

• Mutation frequencies can be calculated from the frequency of the homozygous recessive genotypic class alone.
• The mutation rate is equal to the allelic frequency of the recessive allele divided by the initial frequency of the recessive allele.
• Except in situations of Hardy–Weinberg equilibrium, mutation plays a significant role in changing allelic frequencies.
• Mutation is a major force in generating genetic variability, but by itself plays a relatively insignificant role in changing allelic frequencies.

Answer 18

Mutation is a major force in generating genetic variability, but by itself plays a relatively insignificant role in changing allelic frequencies.

(Mutation creates new alleles and therefore variability. Changes in allele frequencies depend on the forces of natural selection and genetic drift.)

Question 19

Suppose that a given gene undergoes a mutation to a dominant allele such that 2 out of 100,000 offspring exhibit the new mutant phenotype. Assuming that these offspring are heterozygous, what is the mutation rate for the gene?

Answer 19

1/100,000

Question 20

Describe the effects natural selection has on a population.

Answer 20

• consistently causes a population to become better adapted to its environment
• a result of differential success in reproduction
• cannot cause a harmful allele to become more common

(Natural selection is the result of differential survival and reproduction. It is the only mechanism of evolution that consistently causes a population to become better adapted to its environment.)

Question 21

Describe the effects genetic drift has on a population.

Answer 21

• responsible for the founder effect
• responsible for the bottleneck effect
• causes allele frequencies to fluctuate randomly

(Genetic drift describes evolution due to chance events and causes unpredictable fluctuations in allele frequencies. Genetic drift can have a particularly significant effect in a small population, such as during a bottleneck or founder event.)

Question 22

Describe the effects gene flow has on a population.

Answer 22

• can introduce new alleles into a population’s gene pool
• a result of the movement of fertile individuals or their gametes

(Gene flow results when alleles are transferred into or out of a population due to the migration of fertile individuals or their gametes. Gene flow can bring new alleles (beneficial, harmful, or neutral) into a population.)

Question 23

Event or condition: during an extreme heat wave, plants with white flowers survive better.

Which mechanism of evolution is at work?
How does this event affect the population’s gene pool? Do the frequencies of the two alleles change, and if so, how?

Answer 23

Mechanism: natural selection

Effect on allele frequencies: frequency of white allele increases

Question 24

Event or condition: A person uproots the five closest plants, which all happen to have white flowers.

Which mechanism of evolution is at work?
How does this event affect the population’s gene pool? Do the frequencies of the two alleles change, and if so, how?

Answer 24

Mechanism: genetic drift

Effect on allele frequencies: frequency of purple allele increases.

Question 25

Event or condition: A storm kills many plants at random.

Which mechanism of evolution is at work?
How does this event affect the population’s gene pool? Do the frequencies of the two alleles change, and if so, how?

Answer 25

Mechanism: genetic drift

Effect on allele frequencies: allele frequencies change but not predictably

Question 26

Event or condition: Plants with purple flowers attract more insects, which pollinate the plants.

Which mechanism of evolution is at work?
How does this event affect the population’s gene pool? Do the frequencies of the two alleles change, and if so, how?

Answer 26

Mechanism: natural selection

Effect on allele frequencies: frequency of purple allele increases

Question 27

Event or condition: Workers from a nearby greenhouse track white flower seeds into this population’s habitat.

Which mechanism of evolution is at work?
How does this event affect the population’s gene pool? Do the frequencies of the two alleles change, and if so, how?

Answer 27

Mechanism: gene flow

Effect on allele frequencies: frequency of white allele increases

Question 28

True or False?

Genetic drift is primarily associated with relatively small breeding populations.

Answer 28

True.

Question 29

True or False?

Inbreeding by itself can change gene frequencies.

Answer 29

False.

Question 30

Which general term is used to group various biological and behavioral properties of organisms that act to prevent or reduce interbreeding?

• allopatric speciation
• phyletic evolution
• reproductive isolating mechanisms
• genetic divergence
• Inbreeding

Answer 30

Reproductive isolating mechanisms.

Question 30

Which general term is used to group various biological and behavioral properties of organisms that act to prevent or reduce interbreeding?

• allopatric speciation
• phyletic evolution
• reproductive isolating mechanisms
• genetic divergence
• Inbreeding

Answer 30

Reproductive isolating mechanisms.

Question 31

All EXCEPT which of the following mechanisms can work as prezygotic reproductive isolating mechanisms?

• temporal
• behavioral
• hybrid sterility
• mechanical

Answer 31

Hybrid sterility.

(In this case, fertilization does occur and leads to offspring that are sterile. Since fertilization does occur, this is a postzygotic mechanism.)

Question 32

All EXCEPT which of the following mechanisms can work as prezygotic reproductive isolating mechanisms?

• temporal
• behavioral
• hybrid sterility
• mechanical

Answer 32

Hybrid sterility.

(In this case, fertilization does occur and leads to offspring that are sterile. Since fertilization does occur, this is a postzygotic mechanism.)

Question 33

Molecular clocks are used to ________.

• date various fossils
• determine evolutionary relatedness by assessing the molecular relatedness of different organisms
• track the amount of time for species to become extinct
• alter the rates of mutation in different species

Answer 33

Determine evolutionary relatedness by assessing the molecular relatedness of different organisms.

(The molecular clock is based on amino acid or nucleotide differences that occur between different species. The more differences, the less closely related are the two species; the fewer differences, the more closely related.)

Question 34

True or False?

Conservation of amino acid sequence among distantly related groups of organisms is suggestive of an important function of that sequence.

Answer 34

True.

Question 35

True or False?

Evolution is dependent on genetic diversity in the evolving population.

Answer 35

True.