Chapter 23
intersexual selection
A form of natural selection in which individuals of one sex (usually the females) are choosy in selecting their mates from the other sex; also called mate choice.
intrasexual selection
A form of natural selection in which there is direct competition among individuals of one sex for mates of the opposite sex.
the bottleneck effect
A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________. natural selection the founder effect gene flow the bottleneck effect random mating
a few mosquitoes were probably resistant to the insecticide before it was ever used, and these individuals were more likely to survive and reproduce in the presence of insecticide
A number of mosquito populations today are resistant to insecticides that were once quite effective. Biologists think that insecticide resistance evolved in mosquitoes because __________. a few mosquitoes were probably resistant to the insecticide before it was ever used, and these individuals were more likely to survive and reproduce in the presence of insecticide mosquitoes attempted to adapt to their environment individual mosquitoes built up an immunity to an insecticide after being exposed to it mosquitoes needed to develop insecticide resistance to survive after the insecticide was used a new allele developed in response to the insecticide that provided future generations the benefit of resistance
genetic drift
A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to __________. natural selection gene flow mutation genetic drift sexual selection
disruptive 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? Hardy-Weinberg equilibrium directional selection balancing selection disruptive selection stabilizing selection
null hypothesis
A prediction that there is no change, or nothing happening.
genetic drift
A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of this are most pronounced in small populations.
sexual selection
A process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates.
the founder 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 __________. gene flow the founder effect natural selection mutation the bottleneck effect
natural selection
All of the following conditions are required for Hardy-Weinberg equilibrium except __________. natural selection no mutation no gene flow random mating a large population
All of the listed responses are correct.
Allele frequencies can be altered by __________. SHOW HINT natural selection genetic drift gene flow All of the listed responses are correct. None of the listed responses is correct.
bottleneck effect
An earthquake hits a small island. All but a small group of closely related lizards are eliminated, and the survivors spread out over the island. This is an instance of __________. mutation founder effect natural selection bottleneck effect gene flow
Directional selection
Antibiotic resistance in bacteria is an example of which of the following? Directional selection Disruptive selection Macroevolution Stabilizing selection Hardy-Weinberg equilibrium
directional selection
Antibiotic resistance in bacteria is an example of which of the following? Hardy-Weinberg equilibrium disruptive selection macroevolution stabilizing selection directional selection
about 4%
Approximately 1 out of every 2,500 Caucasians in the United States is born with the recessive disease cystic fibrosis. According to the Hardy-Weinberg equilibrium equation, approximately what percentage of people are carriers? about 2% about 96% about .08% about 10% about 4%
0.11
Assume a population in Hardy-Weinberg equilibrium with these genotypic frequencies: AA = 0.25, Aa = 0.50, and aa = 0.25. If you remove all the homozygous dominants and allow the remaining population to reproduce (again under Hardy-Weinberg conditions), what will be the frequency of homozygous dominants in the next generation? 0 0.11 0.22 0.44 0.50
Whole-gene
At what level does gene variability quantify genetic variation? Species Population Whole-gene Individual Molecular
stabilizing selection
Birds with average-size wings survived a severe storm more successfully than other birds in the same population with longer or shorter wings. If severe storms occur regularly, then over time, one should expect these storms to bring about __________. gene flow directional selection the bottleneck effect disruptive selection stabilizing selection
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
Consider a gene that exists in two allelic forms in a simple Mendelian dominant/recessive pair. 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 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 remain the same, 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 go down, and the frequency of the homozygous recessives will go up
genetic variation
Differences among individuals in the composition of their genes or other DNA segments.
sexual dimorphism
Differences between the secondary sex characteristics of males and females of the same species.
adaptive evolution
Evolution that results in a better match between organisms and their environment.
microevolution
Evolutionary change below the species level; change in the allele frequencies in a population over generations.
strains of microorganisms that are resistant to these drugs will be selected for
For several years, scientists have warned doctors of the danger of overprescribing antibiotics such as penicillin. Scientists are concerned because __________. the drugs will be metabolized more quickly by our bodies, decreasing their effectiveness strains of microorganisms that are resistant to these drugs will be selected for the organisms that produce many of the antibiotics are overexploited and could become extinct humans will become tolerant to the effects of drugs None of the listed responses is correct.
founder effect
Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.
bottleneck effect
Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.
neutral variation
Genetic variation that does not provide a selective advantage or disadvantage.
heterozygote advantage
Greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool.
Chance and the environment interact with natural selection, so that the best available traits are selected for.
How does natural selection fashion organisms? The best traits for the current environment arise in the population and are selected for. Brand new body plans arise often, giving natural selection many new possibilities to work with. Neutral traits are often selected for because they will eventually produce alleles that confer an advantage. Chance and the environment interact with natural selection, so that the best available traits are selected for. Sexual selection acts to make organisms better adapted to their environments.
32%
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? 80% 16% 4% 20% 32%
0.9
In a large population of bonobos, the frequency of the recessive allele is initially 0.1. There is no migration and no selection. What is the frequency of the dominant allele? Assume that there are two alleles of this gene. 0.1 0.2 0.5 0.9 0.99
0.9
In a population in Hardy-Weinberg equilibrium, 1% of the individuals in a population show the recessive trait of a certain characteristic. In this situation, what is the value of p? 0.99 0.9 0.81 0.18 The answer cannot be determined from the information given.
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 dominant allele in this population? 0.8 0.64 1 0.04 0.2
0.8
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? 0.64 0.8 0.2 0.36 1
the expected frequency of the heterozygous genotype
In the Hardy-Weinberg equation, 2pq represents __________. the expected frequency of the dominant allele the expected frequency of the homozygous dominant genotype the expected frequency of the heterozygous genotype the expected frequency of the recessive allele the expected frequency of the homozygous recessive genotype
the expected frequency of homozygous dominant individuals in the population
In the Hardy-Weinberg equation, p2 represents __________. the frequency of homozygous recessive individuals in the population the frequency of heterozygous individuals in the population the total alleles in the gene pool the frequency of dominant alleles in the population the expected frequency of homozygous dominant individuals in the population
the expected frequency of the homozygous recessive genotype
In the Hardy-Weinberg equation, q2 represents __________. the expected frequency of the recessive allele 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 heterozygous genotype
Evolution is a change in a population's allele frequencies over generations.
In the context of populations, how do we define evolution? Evolution is the explanation for how organic molecules formed from inorganic molecules. 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 always caused by natural selection. Evolution is a change in a population's allele frequencies over generations.
Evolution is a change in a population's allele frequencies over generations.
In the context of populations, how do we define evolution? Evolution is the tendency for some individuals in a population to leave more offspring than others. Evolution is always caused by natural selection. Evolution is the way in which sexual reproduction can rapidly spread advantageous traits throughout a population. Evolution is a change in a population's allele frequencies over generations. Evolution is the explanation for how organic molecules formed from inorganic molecules.
the sum of the frequencies of the genotypes for a particular gene locus
In the equation for Hardy-Weinberg equilibrium, 1 represents __________. the sum of the frequencies of the genotypes for a particular gene locus the frequency of heterozygous individuals in the populations all the possible phenotypes in the population the frequency of homozygous recessive individuals in the population the frequency of homozygous dominant individuals in the population
directional selection
Natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals.
disruptive selection
Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.
stabilizing selection
Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.
All of the listed responses are correct.
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? Adaptations are often compromises. All of the listed responses are correct. Evolution is limited by historical constraints. Chance, natural selection, and the environment interact. Selection can act only on existing variations.
balancing selection
Natural selection that maintains two or more phenotypic forms in a population.
the reshuffling of alleles in sexual reproduction
No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is __________. geographic variation within the population genetic drift due to the small size of the population environmental effects new mutations that occurred in the preceding generation the reshuffling of alleles in sexual reproduction
neutral variation
Point mutations in noncoding regions of DNA result in __________. gene variability None of the listed responses is correct. protein variability population variation phenotypic variation neutral variation
frequency-dependent selection
Selection in which the fitness of a phenotype depends on how common the phenotype is in a population.
sexual selection
Selection that acts over evolutionary time to preserve traits that increase an individual's ability to mate is known as __________. directional selection sexual selection stabilizing selection balancing selection disruptive selection
meiosis
Sexual recombination includes the shuffling of chromosomes in __________ and fertilization. genetic drift mitosis meiosis mutation natural selection
favors intermediate variants in a population
Stabilizing selection __________. usually results in two distinct phenotypes prevents mutations from occurring occurs only in plants occurs when some individuals migrate to an area with different environmental conditions favors intermediate variants in a population
gene pool
The aggregate of all copies of every type of allele at all loci in every individual in a population. The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population.
relative fitness
The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.
all copies of every type of allele at every locus in all members of the population
The gene pool of a population consists of __________. 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 all of the genes in a single organism only the gene loci that are homozygous only the gene loci that exhibit variation within the population only the gene loci that are heterozygous
0.1%
The human genome consists of approximately 3 billion base pairs. If humans typically differ from one another by about 3 million base pairs, what is the nucleotide variability of Homo sapiens? 0.1% 3% 1% 50% 10%
Heterozygous individuals will survive and may pass the recessive allele on to their offspring.
The lethal genetic disorder Tay-Sachs disease occurs in individuals with two copies of a recessive allele of the responsible gene. Which of the following statements is true? Heterozygous individuals will survive and may pass the recessive allele on to their offspring. Homozygous dominant individuals will be more likely to reproduce than heterozygous individuals. Only homozygous dominant individuals will be able to survive and reproduce. In the heterozygous condition, the dominant allele will overcome the recessive allele and only the dominant allele will be passed on to offspring. Because homozygous recessive individuals die, the recessive allele will eventually be lost from the population.
the heterozygote advantage
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 __________. genetic drift the heterozygote advantage the homozygous recessive advantage gene flow the homozygous dominant advantage
Hardy-Weinberg equilibrium
The state of a population in which frequencies of alleles and genotypes remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.
gene flow
The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes.
Neutral variation increases genetic variation, allowing a population to carry more alleles that may help it respond to environmental change.
What is the importance of neutral variation in evolution? Neutral variation is usually removed from the population by natural selection because it does not confer an advantage in the current environment. Relative frequencies of neutral variations are controlled by natural selection. Many mutations are silent and do not affect the amino acid that is coded for. DNA forensics relies on neutral variation among humans. Neutral variation increases genetic variation, allowing a population to carry more alleles that may help it respond to environmental change.
Mutation
Which of the following can form entirely new alleles? Sexual recombination The environment Mutation Natural selection Genetic drift
Wind blows pollen from one population of plants to another and cross-fertilization occurs.
Which of the following is the best example of gene flow? A small population of humans colonizes a newly formed island. Genes are shuffled by the crossing over of chromosomes during meiosis. 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. An earthquake results in the formation of a canyon, splitting a population of toads apart.
Wind blows pollen from one population of plants to another and cross-fertilization occurs.
Which of the following is the best example of gene flow? 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. Genes are shuffled by the crossing over of chromosomes during meiosis. A small population of humans colonizes a newly formed island. Wind blows pollen from one population of plants to another and cross-fertilization occurs.
mutation
Which of the following mechanisms can form entirely new alleles? mutation genetic drift sexual recombination the environment natural selection
how many fertile offspring it produces
Which of the following most accurately measures an organism's fitness? its mutation rate how strong the organism is when pitted against others of its species how much food it is able to make or obtain its ability to withstand environmental extremes how many fertile offspring it produces
A colony of humans on the moon is isolated from Earth.
Which of the following scenarios would most likely result in the microevolution of a population of humans? A colony of humans on the moon is isolated from Earth. Only random mating takes place among all the people that reproduce in North America. The incidence of skin cancer in adults over age 40 rises significantly. Hundreds of thousands of people are killed in a natural disaster. All of the listed responses are correct.
random mating, no natural selection, and a large population
Which of the following sets of conditions is required for Hardy-Weinberg equilibrium? random mating, no natural selection, and a large population no mutations, no natural selection, with sexual selection random mating, a small population, and no mutations a large population, random mutations, and no migration of alleles in or out of the population a large population, no mutations, with natural selection
All of the listed responses are correct.
Which of the following statements correctly describe(s) characteristics of genetic drift? It can cause allele frequencies to change at random. It can lead to a loss of genetic variation in a population. It is significant in small populations. It can cause harmful alleles to become fixed in a population. All of the listed responses are correct.
Allele and genotype frequencies in the population will remain constant from generation to generation.
Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium? The population is evolving. All of the listed responses are correct. Allele and genotype frequencies in the population change from generation to generation. Allele and genotype frequencies in the population will remain constant from generation to generation. The population exhibits no genetic variation.
Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population.
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. Female mate choice is random, and the showier males happen to be chosen by the females as mates. Showy males are larger and kill off the plain-colored males. Male peacocks with showy feathers have no selective advantage over plain-colored males. Female peacocks choose the plain-colored males as mates, causing this trait to be more prevalent in the population.
human fingerprints
Which of the following would seem to be an example of neutral variation? polymorphism of the Galápagos finches human fingerprints homozygosity in some prairie chicken populations moth coloration founder effect right answer feedback:
Sexual selection can result in sexual dimorphism—marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.
Which statement below is true about sexual selection? There is no evidence that intrasexual selection takes place between females. Showy secondary sexual characteristics cannot be explained because they break all of the rules of natural selection. 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. In most vertebrates, females court the males.
duplication
Which type of mutation plays the most important role in increasing the number of genes in the gene pool? changes in nucleotide sequence point mutation duplication Mutations are so rare that there are no mutations that can have such an important effect. rearrangement of gene loci
Balancing selection
Which type of selection maintains stable frequencies of two or more phenotypic forms in a population? Heterozygote advantage Balancing selection Directional selection Neutral variation Stabilizing selection
balancing selection
Which type of selection maintains stable frequencies of two or more phenotypic forms in a population? heterozygote advantage neutral variation directional selection stabilizing selection balancing selection
Mutation ... sexual recombination ... natural selection
__________ and __________ generate variation, whereas __________ results in an adaptation to the environment. Genetic drift ... natural selection ... mutation Overproduction of offspring ... mutation ... sexual recombination Mutation ... sexual recombination ... natural selection Natural selection ... mutation ... sexual recombination Sexual recombination ... natural selection ... overproduction
inter
between
microevolution
changes in gene frequencies over time
intra
within
