BIOL 1202 - Chapter 23 Mastering Biology
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 - 0.1 - 0.5 - 80
0.4 (The calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20 + 80 + 100) total individuals = 0.4, the frequency of the A1A2 genotype.)
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? - 0.36 - 0.80 - 0.64 - 0.75
0.80
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype? - 0.32 - 0.81 - 0.20 - 0.42 - Genotype frequency cannot be determined from the information provided.
0.81
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool. With respect to the sickle-cell allele, what should be true of the β hemoglobin locus in U.S. populations of African-Americans whose ancestors were from equatorial Africa? 1. The average heterozygosity at this locus should be decreasing over time. 2. There is an increasing heterozygote advantage at this locus. 3. Diploidy is helping to preserve the sickle-cell allele at this locus. 4. Frequency-dependent selection is helping to preserve the sickle-cell allele at this locus. - 1 only - 1 and 3 - 2 and 3 - 1, 2, and 3 - 1, 2, and 4
1 and 3
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. - immigration - sexual reproduction - sexual selection - genetic drift - mutation
sexual reproduction (Sexual reproduction does not change the frequency of alleles in the gene pool.)
Heterozygote advantage should be most closely linked to which of the following? - sexual selection - disruptive selection - directional selection - stabilizing selection - random 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 - stabilizing selection - disruptive selection - directional selection
stabilizing selection
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool. Although selection is clearly present, if the ideal equilibrium of alleles existed, what should be the proportion of heterozygous individuals in populations that live here? - 0.32 - 0.80 - 0.04 - 0.16 - 0.20
0.32
Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies? - Inbreeding - Mutation - Selection - There is no evolutionary force that results in adaptive changes in allele frequencies.
Selection (Selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.)
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? - gene flow - nonrandom mating - genetic drift - natural selection - mutation
genetic drift
Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called? - directional selection - genetic drift - gene flow
genetic drift (Genetic drift is due to chance events that alter allele frequencies.)
Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans. - genetic drift - disease - natural selection - mutation - gene flow
genetic drift (Modern travel and migration decreases the chances of there being a small, isolated population.)
What is the only evolutionary mechanism that consistently leads to adaptive evolution? - the bottleneck effect - genetic drift - gene flow - neutral variation - natural selection
natural selection (Because natural selection has a "sorting" effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.)
Genetic drift is a process based on _____. - emigration - differential reproductive success correlated to the relationship between a phenotype and the environment - mutation - immigration - the role of chance
the role of chance
In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All ten of the original colonists had free earlobes, and two were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes. Which of these is closest to the allele frequency in the founding population? - 0.1 a, 0.9 A - 0.5 a, 0.5 A - 0.8 a, 0.2 A - 0.4 a, 0.6 A - 0.2 a, 0.8 A
0.1 a, 0.9 A
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What is the estimated frequency of allele A in the gene pool? - 0.50 - 0.75 - 0.125 - 0.25
0.50
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What proportion of the population is probably heterozygous (Aa) for this trait? - 0.75 - 0.25 - 0.05 - 0.50
0.50
The ease with which humans travel across the globe is likely to increase _____. - mutation - gene flow - natural selection - genetic drift - all of these
gene flow (When people travel or migrate, they take their alleles with them.)
Homologous pairs of chromosomes are lined up independently of other such pairs during _____. - metaphase II - telophase II - metaphase I - prophase II - anaphase I
metaphase I
Crossing over, resulting in an increase in genetic variation, occurs between _____. - nonsister chromatids of homologous chromosomes - sister chromatids of nonhomologous chromosomes - nonsister chromatids of nonhomologous chromosomes - sister chromatids of homologous chromosomes - sex cells and somatic cells
nonsister chromatids of homologous chromosomes (This process produces chromosomes containing genes inherited from both parents.)
All the genes in a population are that population's _____. - Hardy-Weinberg - genotype - gene pool - phenotype - fitness
gene pool (All the alleles of all the genes of a population make up a gene pool.)
The evolutionary effects of genetic drift are greatest when _____. - intraspecific competition is weak - sexual selection occurs - intraspecific competition is intense - the population size is large - the population size is small
the population size is small (Changes in the gene pool of a small population are frequently due to genetic drift.)
A mutation occurs when _____. - some individuals leave more offspring than other individuals - individuals leave a population - population sizes are small - individuals enter a population - there is a change in the DNA sequence of a gene
there is a change in the DNA sequence of a gene
Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true? - Each bird evolved a deeper, stronger beak as the drought persisted. - Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted. - The frequency of the strong-beak alleles increased in each bird as the drought persisted. - Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in the previous generation.
Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
In the wild, male house finches (Carpodus mexicanus) vary considerably in the amount of red pigmentation in their head and throat feathers, with colors ranging from pale yellow to bright red. These colors come from carotenoid pigments that are found in the birds' diets; no vertebrates are known to synthesize carotenoid pigments. Thus, the brighter red the male's feathers are, the more successful he has been at acquiring the red carotenoid pigment by his food-gathering efforts (all other factors being equal). During breeding season, one should expect female house finches to prefer to mate with males with the brightest red feathers. Which of the following is true of this situation? - Alleles that promote more efficient acquisition of carotenoid-containing foods by males should increase over the course of generations. - There should be directional selection for bright red feathers in males. - Alleles that promote more effective deposition of -carotenoid pigments in the feathers of males should increase over the course of generations. - Three of the statements are correct. - Two of the statements are correct.
Three of the statements are correct.
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 (These are the five assumptions of the Hardy-Weinberg model.)
Rabbit ear size tends to decrease as latitude increases. This is an example of _____. - genetic drift - polymorphism - a cline - heterozygote advantage - artificial selection
a cline (A cline is a gradual change in a trait along a geographic axis.)
A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of - geographic variation. - a cline. - relative fitness. - genetic drift. - a bottleneck.
a cline.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool. The sickle-cell allele is pleiotropic (i.e., it affects more than one phenotypic trait). Specifically, this allele affects oxygen delivery to tissues and affects one's susceptibility to malaria. Under conditions of low atmospheric oxygen availability, individuals heterozygous for this allele can experience life-threatening sickle-cell "crises." Such individuals remain less susceptible to malaria. Thus, pleiotropic genes/alleles such as this can help explain why - chance events can affect the evolutionary history of populations. - new advantageous alleles do not arise on demand. - evolution is limited by historical constraints. - adaptations are often compromises.
adaptations are often compromises.
Which variable is likely to undergo the largest change in value resulting from a mutation that introduces a new allele into a population at a locus for which all individuals formerly had been fully homozygous? - geographic variability - average heterozygosity - average number of loci - nucleotide variability
average heterozygosity
Evolution - must happen, due to organisms' innate desire to survive. - can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met. - must happen whenever a population is not well-adapted to its environment. - requires the operation of natural selection. - requires that populations become better suited to their environments.
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 _____. - genetic variability - contribution to the gene pool of the next generation - mutation rate - health - stability in the face of environmental change
contribution to the gene pool of the next generation (Those organisms with adaptations best suited to the current environment will make the most significant contribution to the next generation.)
You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to - reduce the number of flies that you transfer at each generation. - cross your flies with flies from another lab. - change the temperature at which you rear the flies. - transfer only the largest flies. - shock the flies with a brief treatment of heat or cold to make them more hardy.
cross your flies with flies from another lab.
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 _____. - genetic drift - neutral variation - stabilizing selection - directional selection - disruptive selection
directional selection (The characteristics of the poppies shifted in response to the changed environment.)
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool. In the United States, the parasite that causes malaria is not present, but African-Americans whose ancestors were from equatorial Africa are present. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa? - stabilizing selection; disruptive selection - directional selection; stabilizing selection - directional selection; disruptive selection - disruptive selection; stabilizing selection - disruptive selection; directional selection
directional selection; stabilizing selection
What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population? - gene flow - bottleneck effect - mutation - nucleotide variability - founder effect
founder effect (The founder effect is genetic drift attributable to colonization by a limited number of individuals from a parent population.)
If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be - 23%. - 46%. - 54%. - There is not enough information to say.
54%.
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 0.1. - 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 0.3. (The frequency of the A1 allele is p = (number of A1 alleles) / (total of all alleles) = [(2 ( 20) + 80] / [(2 × 20) + (2 × 80) + (2 × 100)] = 0.3.)
You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population? - 0.09 - 0.08 - 0.07 - 0.70 - Allele frequency cannot be determined from this information.
Allele frequency cannot be determined from this information.
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? - 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. - The mutation rate will increase. - Alleles that promote "tallness" will decrease in frequency. - Gene flow will increase.
Alleles that promote "tallness" will decrease in frequency. (A reduction in "tallness" alleles is the change expected as a result of this type of selection.)
Which statement about variation is true? - All geographic variation results from the existence of clines. - All genetic variation produces phenotypic variation. - All phenotypic variation is the result of genotypic variation. - All nucleotide variability results in neutral variation. - None of the above
None of the above
Hardy-Weinberg equilibrium must occur in populations wherein - natural selection is not operating. - no genetic variation exists. - an allele remains fixed. - All three of the responses above are correct. - Only two of the responses above are correct.
Only two of the responses above are correct.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool. Again, if this population were in equilibrium and if the sickle-cell allele is recessive, what proportion of the population should be susceptible to sickle-cell anemia under typical conditions? - 0.80 - 0.20 - 0.16 - 0.04 - 0.32
0.04
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? - 9.0 - 0.49 - 0.09 - 49.0 - 0.9
0.09
In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All ten of the original colonists had free earlobes, and two were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes. If one assumes that Hardy-Weinberg equilibrium applies to the population of colonists on this planet, about how many people will have attached earlobes when the planet's population reaches 10,000? - 100 - 1,000 - 10,000 - 400 - 800
100
In a very large population, a quantitative trait has the following distribution pattern: If the curve in the figure shifts to the left or to the right, there is no gene flow, and the population size consequently increases over successive generations. Which of the following is (are) probably occurring? 1. immigration or emigration 2. directional selection 3. adaptation 4. genetic drift 5. disruptive selection - 1, 2, and 3 - 1 only - 4 and 5 - 2 and 3 - 4 only
2 and 3
In human gamete production there is an average of _____ crossover events per chromosome pair. - 2-3 - 9-10 - 5-6 - 0-1 - 10+
2-3 (These crossover events increase the genetic variation among gametes.)
Which of these individuals is a homozygous genotype? - Gg - AG - AA - aG - Aa
AA (When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.)
There are those who claim that the theory of evolution cannot be true because the apes, which are supposed to be closely related to humans, do not likewise share the same large brains, capacity for complicated speech, and tool-making capability. They reason that if these features are generally beneficial, then the apes should have evolved them as well. Which of these provides the best argument against this misconception? - A population's evolution is limited by historical constraints. - Adaptations are often compromises. - Evolution can be influenced by environmental change. - Advantageous alleles do not arise on demand.
Advantageous alleles do not arise on demand.
How many of these statements regarding populations are true? 1. Mature males and females of a population can interbreed with each other. 2. Populations are sometimes geographically isolated from other populations. 3. Biological species are made up of populations. 4. Members of a population tend to be genetically more similar to each other than to members of other populations. 5. Populations have genomes, but not gene pools. - Only one of these statements is true. - Two of these statements are true. - Three of these statements are true. - Four of these statements are true. - All five of these statements are true.
Four of these statements are true.
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, number of individuals in the population - Allele frequencies, phenotype frequencies - Allele frequencies in a subset of the population
Frequencies of two alleles in a gene pool before and after many random matings (Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next.)
Which of the following is a true statement concerning genetic variation? - It arises in response to changes in the environment. - It must be present in a population before evolution can occur in the population. - A population that has a higher average heterozygosity has less genetic variation than one with a lower average heterozygosity. - It tends to be reduced by the processes involved when diploid organisms produce gametes. - It is created by the direct action of natural selection.
It must be present in a population before evolution can occur in the population.
Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur? - If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency. - If the Tamiflu-resistance gene confers no benefit in the current environment, and has no cost, the virus will become dormant until Tamiflu is present. - The Tamiflu-resistance gene will undergo mutations that convert it into a gene that has a useful function in this environment. - The new virus will maintain its Tamiflu-resistance gene, just in case of future exposure to Tamiflu.
If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.
How does diploidy help to preserve genetic variation? - It restricts the gene pool by chance events such as floods or other catastrophic events. - It fosters the exchange of genes between different populations. - 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 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. (Natural selection tends to decrease genetic variation. Recessive alleles are shielded from natural selection in heterozygotes.)
The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur? - Methylated DNA should become fixed in the gene pools of bacterial species. - Nonmethylated DNA should become fixed in the gene pools of bacteriophages. - Methylated DNA should become fixed in the gene pools of bacteriophages. - Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time. - Both the first and second responses are correct.
Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
Which of the following evolutionary forces could create new genetic information in a population? - Mutation - Genetic drift - Nonrandom mating - Selection
Mutation (Mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.)
What is true of natural selection? - 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. - Natural selection creates beneficial mutations. - Natural selection is a random process. - Mutations occur at random; natural selection can preserve and distribute beneficial mutations. - The only way to eliminate harmful mutations is through natural selection.
Mutations occur at random; natural selection can preserve and distribute beneficial mutations.
The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement is correct? - Resistance to DDT evolved in some fruit flies in order to allow them to survive. - The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread. - Alleles for DDT resistance arose by mutation during the period of DDT use because of selection for pesticide resistance.
The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread. (As the environment changed with the increased use of DDT, the advantages of the heritable trait of DDT resistance increased. Natural selection has different effects in different environments.)
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 0.32, 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. - The expected genotype frequencies are 0.33, 0.33, and 0.33 for A1A1, A1A2 , and A2A2 , respectively. - 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 frequency of the A1A1 genotype is p 2 = (0.8)(0.8) = 0.64; the expected frequency of the A1A2 genotype is 2pq = 2(0.8)(0.2) = 0.32; the expected frequency of the A2A2 genotype is q 2 = (0.2)(0.2) = 0.04. To verify your calculations, confirm that the three frequencies add up to one.)
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 p 2, 2pq, and q 2 for generation after generation. - When alleles are transmitted according to the rules of Mendelian inheritance, their frequencies do not change over time. - The genotype frequencies in the offspring generation must add up to two. - 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. (This statement is not true; the genotype frequencies in the offspring generation must add up to one.)
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time? - There has been a high rate of mutation of allele A to allele a. - The genotype AA is lethal. - The two phenotypes are about equally adaptive under laboratory conditions. - There has been sexual selection favoring allele a. - The population is undergoing genetic drift.
The two phenotypes are about equally adaptive under laboratory conditions.
In the formula for determining a population's genotype frequencies, the 2 in the term 2pq is necessary because - heterozygotes have two alleles. - the population is doubling in number. - the population is diploid. - heterozygotes can come about in two ways.
heterozygotes can come about in two ways.
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 - 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 has not had sufficient time to create the optimal design in each case, but will do so given enough time. - in many cases, phenotype is not merely determined by genotype, but by the environment as well. - natural selection is generally limited to modifying structures that were present in previous generations and in previous species.
natural selection is generally limited to modifying structures that were present in previous generations and in previous species.
You are studying three populations of birds. Population A has ten birds, of which one is brown (a recessive trait) and nine are red. Population B has 100 birds, of which ten are brown. Population C has 30 birds, and three of them are brown. In which population would it be least likely that an accident would significantly alter the frequency of the brown allele? - population A - population B - population C - They are all the same. - It is impossible to tell from the information given.
population B
