Chapter 23

Which type of mutation plays the most important role in increasing the number of genes in the gene pool? ANSWER Duplication Mutations are so rare that there are no mutations that can have such an important effect. Point mutation Rearrangement of gene loci Changes in nucleotide sequence

Duplication

A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________. ANSWER the bottleneck effect the founder effect gene flow natural selection random mating

the bottleneck effect

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 __________. ANSWER the founder effect the bottleneck effect gene flow natural selection mutation

the founder effect

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? ANSWER 0.2 0.8 0.64 0.04 1

0.2

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? ANSWER 0.8 0.64 1 0.36 0.2

0.8

In a certain group of African people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group has the selective advantage of being more resistant to malaria (heterozygous) than those individuals who are homozygous for normal hemoglobin or for sickle-cell disease? ANSWER 32% 2% 4% 8% 16%

32

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? ANSWER 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.

All of the listed responses are correct

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

All of the listed responses are correct.

Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium? ANSWER Allele and genotype frequencies in the population will remain constant from generation to generation. Allele and genotype frequencies in the population change from generation to generation. The population is evolving. The population exhibits no genetic variation. All of the listed responses are correct.

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

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population? ANSWER Balancing selection Neutral variation Heterozygote advantage Stabilizing selection Directional selection

Balancing selection

Antibiotic resistance in bacteria is an example of which of the following? ANSWER Directional selection Stabilizing selection Disruptive selection Hardy-Weinberg equilibrium Macroevolution

Directional selection

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? ANSWER Disruptive selection Stabilizing selection Directional selection Balancing selection Hardy-Weinberg equilibrium

Disruptive selection

In the context of populations, how do we define evolution? ANSWER Evolution is a change in a population's allele frequencies over generations. Evolution is the tendency for some individuals in a population to leave more offspring than others. Evolution is the way in which sexual reproduction can rapidly spread advantageous traits throughout a population. Evolution is the explanation for how organic molecules formed from inorganic molecules. Evolution is always caused by natural selection.

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

Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors? ANSWER Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population. Female peacocks choose the plain-colored males as mates, causing this trait to be more prevalent in the population. Showy males are larger and kill off the plain-colored males. Female mate choice is random, and the showier males happen to be chosen by the females as mates. Male peacocks with showy feathers have no selective advantage over plain-colored males.

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

Which of the following would seem to be an example of neutral variation? ANSWER Human fingerprints Homozygosity of the cheetah population Polymorphism of the Galápagos finches Founder effect Moth coloration

Human fingerprints

Which of the following sets of conditions is required for Hardy-Weinberg equilibrium? ANSWER Random mating, no natural selection, and a large population A large population, no mutations, with natural selection A large population, random mutations, and no migration of alleles in or out of the population No mutations, no natural selection, with sexual selection Random mating, a small population, and no mutations

Random mating, no natural selection, and a large population

Which statement below is true about sexual selection? ANSWER Sexual selection can result in sexual dimorphism—marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction. Intrasexual selection leads to the death of most unfit males in combat. Showy secondary sexual characteristics cannot be explained because they break all of the rules of natural selection. In most vertebrates, females court the males. There is no evidence that intrasexual selection takes place between females.

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

At what level does gene variability quantify genetic variation? ANSWER Whole-gene Molecular Population Species Individual

Whole-gene

Which of the following is the best example of gene flow? ANSWER Wind blows pollen from one population of plants to another and cross-fertilization occurs. A small population of humans colonizes a newly formed island. Genes are shuffled by the crossing over of chromosomes during meiosis. An earthquake results in the formation of a canyon, splitting a population of toads apart. A fire drastically reduces the size of a white-tailed deer population. The remaining individuals spread out throughout the remaining forest.

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

Stabilizing selection __________. ANSWER favors intermediate variants in a population prevents mutations from occurring occurs when some individuals migrate to an area with different environmental conditions usually results in two distinct phenotypes occurs only in plants

favors intermediate variants in a population

All of the following conditions are required for Hardy-Weinberg equilibrium except __________. ANSWER natural selection a large population no mutation no gene flow random mating

natural selection

Point mutations in noncoding regions of DNA result in __________. ANSWER neutral variation phenotypic variation gene variability population variation molecular variability None of the listed responses is correct.

neutral variation

In the Hardy-Weinberg equation, 2pq represents __________. ANSWER the expected frequency of the heterozygous genotype the expected frequency of the homozygous recessive genotype the expected frequency of the homozygous dominant genotype the expected frequency of the dominant allele the expected frequency of the recessive allele

the expected frequency of the heterozygous genotype

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, __________. ANSWER 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 frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go up, and the frequency of the homozygous recessives will remain the same the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will remain the same, and the frequency of the homozygous recessives will go up the frequency of the homozygous dominants will go up, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go down the frequency of the homozygous dominants will go up, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up

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 __________. ANSWER the heterozygote advantage the homozygous dominant advantage the homozygous recessive advantage genetic drift gene flow

the heterozygote advantage

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is __________. ANSWER the reshuffling of alleles in sexual reproduction new mutations that occurred in the preceding generation genetic drift due to the small size of the population geographic variation within the population environmental effects

the reshuffling of alleles in sexual reproduction

The gene pool of a population consists of __________. ANSWER all copies of every type of allele at every locus in all members of the population only the gene loci that are heterozygous only the gene loci that are homozygous only the gene loci that exhibit variation within the population all of the genes in a single organism all of the genes in the females of a population

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

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization. ANSWER meiosis mitosis genetic drift natural selection mutation

meiosis

Which of the following can form entirely new alleles? ANSWER Mutation Natural selection Genetic drift Sexual recombination The environment

mutation