Chapter 21 Homework
In a population of 200 mice, brown fur is dominant to gray fur. If 120 of the 200 mice have brown fur, what is the frequency of mice that are heterozygous?
0.46
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? a) 0.09 b) 0.49 c) 0.9 d) 9.0
a) 0.09
Phenylketonuria (PKU) is a birth defect that causes an amino acid called phenylalanine to build up in the body. The frequency of individuals born in a population with PKU is q2. There is one PKU (q2) birth per 10,000 births. The frequency of the recessive allele for PKU in this population is q = 0.01. The frequency of the dominant allele in this population is p = 1 - q = 0.99. What is the frequency of carriers (2pq) in this population? a) 2% b) 1% c) 3% d) 4%
a) 2%
How can gene flow improve adaptation of population? a) Beneficial alleles are transferred to a new population b) Allele frequencies decrease in new population c) Alleles increase in frequency in original population d) Alleles mutate in different geographical areas
a) Beneficial alleles are transferred to a new population
Why is the Hardy-Weinberg model useful? a) It allows you to calculate genotype frequencies of a population and compare them to what was expected under the assumptions b) It is used under the assumption that natural selection is occurring, thus providing a quantitative method to detect genetic drift in a population c) It allows you to get an accurate count of the total population size d) It allows you to get a total count of all individuals in a population and compare those values to an equilibrium.
a) It allows you to calculate genotype frequencies of a population and compare them to what was expected under the assumptions
Which of the following is correct about genetic variation? a) It must be present in a population before natural selection can act upon the population b) It arises in response to changes in the environment c) It is created by the direct action of natural selection d) It tends to be reduced when diploid organisms produce gametes and reproduce
a) It must be present in a population before natural selection can act upon the population
Why don't similar genotypes always produce the same phenotype? a) Phenotypes can vary depending upon environment b) Parents alter their phenotypes and pass on this phenotype to progeny c) Animals display different phenotypes dependent on diet, not genotype d) Genetic variants of ADH enzyme produce the same phenotype
a) Phenotypes can vary depending upon environment
Mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology. In Tibet, for example, people have broader arteries and capillaries. In the Andes, they can dissolve more oxygen into their blood. These different traits of people who live in high altitudes illustrate... a) adaptive evolution b) acclimatization c) sexual selection d) stabilizing evolution
a) adaptive evolution
What is the Hardy-Weinberg equation? a) an assessment of evolution at a particular locus b) a determination of allele frequency c) a determination of genotype frequency d) an assessment of heterozygosity in a population
a) an assessment of evolution at a particular locus
In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?
0.8
How did Mendel's model of inheritance help explain Darwin's theory of natural selection? a) by proposing a mechanism of how organisms could transmit discrete, heritable units to offspring b) by observations of individuals' differences in traits c) by explaining the natural selection of genetic differences among offspring d) by leading to an evolutionary change
a) by proposing a mechanism of how organisms could transmit discrete, heritable units to offspring
Evolution of a gene.. a) can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met for that particular gene b) requires the operation of natural selection c) must happen whenever a population is not well adapted to its environment d) must happen, due to organisms' innate desire to survive
a) can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met for that particular gene
In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population? a) directional selection b) disruptive selection c) stabilizing selection d) No selection would operate because the population is in Hardy-Weinberg equilibrium
a) directional selection
Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing... a) gene flow b) genetic drift c) nonrandom mating d) geographic isolation
a) gene flow
The Hardy-Weinberg equation p2 + 2pq + q2 = 1 allows you to calculate... a) genotype frequencies b) population declines c) genome frequencies d) population abundance and mating patterns
a) genotype frequencies
In the formula for determining a population's genotype frequencies, the 2 in the term 2pq is necessary because... a) heterozygotes can come about in two ways based upon parental gametes b) the population is diploid c) the population is doubling in number d) heterozygotes have two alleles
a) heterozygotes can come about in two ways based upon parental gametes
What is the result of adaptive evolution? a) increase in frequency of alleles that provide reproductive advantage b) survival of the fittest c) sorting by natural selection d) formation of new genetic variants
a) increase in frequency of alleles that provide reproductive advantage
Sexual dimorphism is most often a result of... a) intersexual selection b) artificial selection c) intrasexual selection d) stabilizing selection e) pansexual selection
a) intersexual selection
It is estimated by a wide body of scientists that in recent decades we have begun another mass extinction event on Earth. Amphibians in particular have been in decline, sometimes due to climate change, and they therefore provide a possible early sign of dramatic biodiversity change to come. With respect to climate change and natural selection acting upon a population of one species of frog in a tropical rain forest, mutations of DNA sequences of the frog genome that are inherited by offspring a) may have no effect at all, be beneficial, or be harmful b) will only speed the decline and extinction of the species c) will primarily be harmful d) could either be beneficial or harmful
a) may have no effect at all, be beneficial, or be harmful
Which of the following consistently improves the degree to which organisms are well suited for life in their environment? a) natural selection b) adaptation c) gene flow d)genetic drift
a) natural selection
Heterozygote advantage should be most closely linked to which of the following? a) stabilizing selection b) sexual selection c) random selection d) directional selection e) disruptive selection
a) 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? a) stabilizing selection b) disruptive selection c) sexual selection d) directional selection e) artificial selection
a) stabilizing selection
Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus... a) the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change b) natural selection, gene flow, and genetic drift are acting equally to change an allele's frequency c) this means that, at this locus, two alleles are present in equal proportions d) the population itself is not evolving, but individuals within the population may be evolving
a) the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change
When evolution occurred on the Galápagos Islands, the finch beaks... a) varied in size across the population and sometimes conferred benefits in feeding, survivorship, and reproduction that were passed down to surviving offspring b) of individual birds in the population changed size and shape between the time of fledging the nest and adulthood due to the environmental stress induced by drought c) had corresponding genetic codes in the DNA that were modified or mutated by individuals when attempting to survive the stressful environment of the drought d) changed in size and depth only during the lifetime of the fittest birds able to survive the drought
a) varied in size across the population and sometimes conferred benefits in feeding, survivorship, and reproduction that were passed down to surviving offspring
What is the founder effect? a) when a few individuals become isolated from a larger population and their gene pool differs from that source population b) a sudden change in the environment that reduces the size of the population c) a series of chance events that change allele frequency d) a selection of the best-suited traits for the environment
a) when a few individuals become isolated from a larger population and their gene pool differs from that source population
