Chapter 21

True or false? The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.

true

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. new mutations that occurred in the preceding generation. genetic drift due to the small size of the population. natural selection. environmental effects.

the reshuffling of alleles in sexual reproduction.

Genetic drift is a process based on _____. mutation immigration the role of chance differential reproductive success correlated to the relationship between a phenotype and the environment emigration

the role of chance

Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing geographic isolation. genetic drift. gene flow. nonrandom mating.

gene flow.

All the genes in a population are that population's _____. gene pool phenotype genotype Hardy-Weinberg fitness

gene pool

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called? gene flow genetic drift directional selection

genetic drift

Although each of the following has a better chance of influencing gene frequencies in small populations than in large populations, which one most consistently requires a small population as a precondition for its occurrence? mutation gene flow genetic drift nonrandom mating natural selection

genetic drift

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans. disease mutation gene flow genetic drift natural selection

genetic drift

Sexual dimorphism is most often a result of pansexual selection. intrasexual selection. intersexual selection. artificial selection. stabilizing selection.

intersexual selection.

The original source of all genetic variation is _____. recombination sexual reproduction natural selection independent assortment mutation

mutation

The ease with which humans travel across the globe is likely to increase _____. genetic drift natural selection mutation gene flow all of these

gene flow

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers? Stabilizing selection Disruptive selection Directional selection

Disruptive selection

According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool. genetic drift sexual selection sexual reproduction mutation immigration

sexual reproduction

Which statement correctly describes the role of chance in evolution? An allele that increases evolutionary fitness cannot be lost from a population by chance events. The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA. Evolution by natural selection proceeds by an accumulation of changes that occur by chance.

The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.

In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following? The number of individuals Time The value of a particular characteristic; characteristics of an organism can include such traits as size and color.

The value of a particular characteristic; characteristics of an organism can include such traits as size and color.

Evolution requires the operation of natural selection. requires that populations become better suited to their environments. must happen whenever a population is not well adapted to its environment. must happen, due to organisms' innate desire to survive. can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.

can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.

In evolutionary terms, an organism's fitness is measured by its _____. contribution to the gene pool of the next generation stability in the face of environmental change health mutation rate genetic variability

contribution to the gene pool of the next generation

Which of the following is most likely to produce an African butterfly species in the wild whose members have one of two strikingly different color patterns? directional selection sexual selection artificial selection stabilizing selection disruptive selection

disruptive selection

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population? Alleles that promote "tallness" will decrease in frequency. The mutation rate will increase. It will increase in number since shorter people use fewer resources than taller people. Genetic drift will play less of a role in the evolution of humans. Gene flow will increase.

Alleles that promote "tallness" will decrease in frequency.

Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards? Disruptive selection Stabilizing selection Directional selection

Stabilizing selection

In human gamete production there is an average of _____ crossover events per chromosome pair. 10+ 0-1 5-6 9-10 2-3

2-3

You read about soapberry bugs and select the correct statement describing relative fitness in these individuals. A soapberry bug with high relative fitness has more mates than other bugs. A soapberry bug with high relative fitness feeds more successfully on fruits than do other bugs. A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.

A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.

Which of these individuals is a homozygous genotype? Aa Gg aG AG AA

AA

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele? 0.49 0.09 49.0 9.0 0.9

0.09

What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals? 0.4 0.5 80 0.1

0.4

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2? 0.21 0.09 0.49 0.42 0.7

0.42

Rank the following one-base-point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide: 1. insertion mutation deep within an intron 2. substitution mutation at the third position of an exonic codon 3. substitution mutation at the second position of an exonic codon 4. deletion mutation within the first exon of the gene 3, 1, 4, 2 2, 1, 4, 3 4, 3, 2, 1 2, 3, 1, 4 1, 2, 3, 4

4, 3, 2, 1

Which statement about variation is true? All phenotypic variation is the result of genotypic variation. All new alleles are the result of nucleotide variability. All geographic variation results from the existence of clines. All genetic variation produces phenotypic variation. All nucleotide variability results in neutral variation.

All new alleles are the result of nucleotide variability.

Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today? Directional selection Disruptive selection Stabilizing selection

Directional selection

Which type of selection tends to increase genetic variation? Stabilizing selection Disruptive selection Directional selection

Disruptive selection

Which of the following are basic components of the Hardy-Weinberg model? Frequencies of two alleles in a gene pool before and after many random matings Allele frequencies, phenotype frequencies Allele frequencies, number of individuals in the population Allele frequencies in a subset of the population

Frequencies of two alleles in a gene pool before and after many random matings

How does diploidy help to preserve genetic variation? It fosters the exchange of genes between different populations. It restricts the gene pool by chance events such as floods or other catastrophic events. It helps individual organisms make a greater contribution to the gene pool of the next generation. It allows the frequency of a recessive allele in a population to be predicted under certain conditions. It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

Which of the following statements best summarizes evolution as it is viewed today? It is the descent of humans from the present-day great apes. It is the differential survival and reproduction of the most-fit phenotypes. It is synonymous with the process of gene flow. It represents the result of selection for acquired characteristics.

It is the differential survival and reproduction of the most-fit phenotypes.

What is true of microevolution? It is evolution that influences only a small subset of the populations that comprise a species. It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations. It is evolution that involves only tiny changes to DNA, such as point mutations, producing only small (if any) changes to phenotype. It is evolution that results in the origin of small numbers of new species. It is evolution that is restricted to individual organisms.

It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations.

Which of the following is a true statement concerning genetic variation? It must be present in a population before natural selection can act upon the population. A population that has a higher average heterozygosity has less genetic variation than one with a lower average heterozygosity. It is created by the direct action of natural selection. It arises in response to changes in the environment. It tends to be reduced by the processes involved when diploid organisms produce gametes.

It must be present in a population before natural selection can act upon the population.

Which of the following evolutionary forces could create new genetic information in a population? Mutation Nonrandom mating Selection Genetic drift

Mutation

What is true of natural selection? Natural selection creates beneficial mutations. Mutations occur when directed by the good of the species; natural selection edits out harmful mutations and causes populations to adapt to the beneficial mutations. The only way to eliminate harmful mutations is through natural selection. Natural selection is a random process. Mutations occur at random; natural selection can preserve and distribute beneficial mutations.

Mutations occur at random; natural selection can preserve and distribute beneficial mutations.

Which of the following evolutionary forces results in adaptive changes in allele frequencies? There is no evolutionary force that results in adaptive changes in allele frequencies. Mutation Selection Nonrandom mating

Selection

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies? Disruptive selection Stabilizing selection Directional selection

Stabilizing selection

What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene? The expected genotype frequencies are 0.25, 0.5, and 0.25 for A1A1, A1A2, and A2A2, respectively. The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2, and A2A2, respectively. The expected genotype frequencies are 0.33, 0.33, and 0.33 for A1A1, A1A2, and A2A2, respectively. The expected genotype frequencies are 0.32, 0.64, and 0.04 for A1A1, A1A2, and A2A2, respectively.

The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2, and A2A2, respectively.

What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals? The frequency of the A1 allele is 0.7. The frequency of the A1 allele is 0.3. The frequency of the A1 allele is 0.5. The frequency of the A1 allele is 0.1.

The frequency of the A1 allele is 0.3.

Which of the following statements is not a part of the Hardy-Weinberg principle? If allele frequencies in a population are given by p and q, then genotype frequencies will be given by p2, 2pq, and q2 for generation after generation. When alleles are transmitted according to the rules of Mendelian inheritance, their frequencies do not change over time. Even if allele A1 is dominant to allele A2, it does not increase in frequency. The genotype frequencies in the offspring generation must add up to two.

The genotype frequencies in the offspring generation must add up to two.

Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____. stabilizing selection directional selection neutral variation disruptive selection

directional selection

True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.

false

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population? founder effect bottleneck effect mutation nucleotide variability gene flow

founder effect

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation most likely resulted from directional selection genetic drift nonrandom mating disruptive selection gene flow

genetic drift

Natural selection changes allele frequencies because some ________ survive and reproduce more successfully than others. individuals alleles loci gene pools species

individuals

Homologous pairs of chromosomes are lined up independently of other such pairs during _____. telophase II anaphase I prophase II metaphase II metaphase I

metaphase I

Generation-to-generation change in the allele frequencies in a population is _____. macroevolution natural selection genetic drift microevolution mutation

microevolution

What is the only evolutionary mechanism that consistently leads to adaptive evolution? natural selection gene flow genetic drift neutral variation the bottleneck effect

natural selection

A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because natural selection is generally limited to modifying structures that were present in previous generations and in previous species. in many cases, phenotype is not merely determined by genotype, but by the environment as well. natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time. though we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design.

natural selection is generally limited to modifying structures that were present in previous generations and in previous species.

Crossing over, resulting in an increase in genetic variation, occurs between _____. sister chromatids of nonhomologous chromosomes nonsister chromatids of nonhomologous chromosomes sex cells and somatic cells sister chromatids of homologous chromosomes nonsister chromatids of homologous chromosomes

nonsister chromatids of homologous chromosomes

Heterozygote advantage should be most closely linked to which of the following? sexual selection directional selection random selection disruptive selection stabilizing selection

stabilizing selection

Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer, or more, than this have reduced fitness. Which of the following terms best describes this situation? artificial selection sexual selection disruptive selection stabilizing selection directional selection

stabilizing selection

Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating disruptive selection. neutral variation. the bottleneck effect. frequency-dependent selection stabilizing selection.

stabilizing selection.

The evolutionary effects of genetic drift are greatest when _____. sexual selection occurs the population size is small intraspecific competition is intense intraspecific competition is weak the population size is large

the population size is small

A mutation occurs when _____. there is a change in the DNA sequence of a gene individuals enter a population some individuals leave more offspring than other individuals population sizes are small individuals leave a population

there is a change in the DNA sequence of a gene