Chapter 23 The Evolution of Populations

At what level does gene variability quantify genetic variation?

whole-gene

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the dominant allele in this population?

0.2

In a certain group of people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group is heterozygous for the sickle hemoglobin allele?

32%

Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium?

Allele and genotype frequencies in the population will remain constant from generation to generation.

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

Disruptive selection

In the context of populations, how do we define evolution?

Evolution is a change in a population's allele frequencies over generations.

Which of the following sets of conditions is required for Hardy-Weinberg equilibrium?

Random mating, no natural selection, and a large population

Which statement below is true about sexual selection?

Sexual selection can result in sexual dimorphism—marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.

Which of the following is the best example of gene flow?

Wind blows pollen from one population of plants to another and cross-fertilization occurs.

The gene pool of a population consists of __________.

all copies of every type of allele at every locus in all members of the population

Antibiotic resistance in bacteria is an example of which of the following?

directional selection

Which of the following would seem to be an example of neutral variation?

human fingerprints

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.

meiosis

Which of the following can form entirely new alleles?

mutation

All of the following conditions are required for Hardy-Weinberg equilibrium except __________.

natural selection

Point mutations in noncoding regions of DNA result in __________.

neutral variation

A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________.

the bottleneck effect

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is __________.

the reshuffling of alleles in sexual reproduction

Which of the following statements correctly describe(s) characteristics of genetic drift?

-All of the listed responses are correct. It is significant in small populations. It can cause allele frequencies to change at random. It can lead to a loss of genetic variation in a population. It can cause harmful alleles to become fixed in a population.

Natural selection leads to adaptation, but there are many organisms on Earth that exhibit characteristics that are less than ideal for their environment. Which of the following statements correctly explain(s) this?

-All of the listed responses are correct. Selection can act only on existing variations. Evolution is limited by historical constraints. Adaptations are often compromises. Chance, natural selection, and the environment interact.

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the recessive allele in this population?

0.8

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

Duplication

Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors?

Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population.

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

balancing selection

Stabilizing selection __________.

favors intermediate variants in a population

In the Hardy-Weinberg equation, 2pq represents __________.

the expected frequency of the heterozygous genotype

In the Hardy-Weinberg equation, q2 represents __________.

the expected frequency of the homozygous recessive genotype

A storm separates a small number of birds in a migrating population. These birds end up at a destination different from where they usually migrate and establish a new population in this new area. This is an example of __________.

the founder effect

In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.

the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up

The sickle-cell allele, which is recessive, causes anemia but confers resistance to malaria in individuals who possess it. However, homozygous recessive individuals often die from anemia but not from malaria, and homozygous dominant individuals do not have anemia but could die from malaria. Heterozygous individuals have the highest relative fitness. This is an example of __________.

the heterozygote advantage