A large population of laboratory animals has been allowed to breed without human interference 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?
The two phenotypes are about equally adaptive under laboratory conditions.
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
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?
Allele frequency cannot be determined from this information.
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?
0.32
Martin Wikelski and L. Michael Romero (Body size, performance and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]:376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females.
stabilizing selection
Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.
gene flow
Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then _____.
sexual dimorphism was evolving over time in these species
An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?
a genetic bottleneck
Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is TRUE?
Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
Which of these is NOT a mechanism that contributes to genetic variation within a population of sexually reproducing organisms?
mutation in somatic (body) cells
For a biologist studying a small fish population in the lab, which Hardy-Weinberg condition is easiest to meet?
no gene flow
In 1983 a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.) The UCSD campus male junco population tails are about 36% white, whereas the tails of males from nearby mountain populations are about 40-45% white. The founding stock of UCSD birds was likely from the nearby mountain populations because some of those birds overwinter on the UCSD campus each year. Population sizes on the UCSD campus have been reasonably large, and there are significant habitat differences between the UCSD campus and the mountain coniferous forests; UCSD campus has a more open environment (making birds more visible) and a lower junco density (decreasing intraspecific competition) than that in the mountain forests. Given this information, which of the following evolutionary mechanisms do you think is most likely responsible for the difference between the UCSD and mountain populations?
natural selection
In the formula for determining a population's genotype frequencies, the "pq" in the term 2pq is necessary because _____.
heterozygotes have two alleles
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?
0.09
Which of the following is the most predictable outcome of increased gene flow between two populations?
decreased genetic difference between the two populations
In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?
Mutation led to increased genetic variation.
Currently the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferably catch and eat slower iguanas are introduced to the island, iguana body size is likely to _____ in the absence of other factors; the iguanas would then be under _____ selection.
decrease; directional
If, on average, 46% of the loci in any given individual of a particular species are heterozygous, then the average homozygosity of the species should be _____.
54%
Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by _____.
the founder effect
Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, _____.
the frequencies of alleles at that locus should not change from one generation to the next
Most Swiss starlings produce four to five eggs in each clutch. Starlings producing either fewer or more eggs than this have reduced fitness. Which of the following terms best describes this situation?
stabilizing selection
Cystic fibrosis is a human genetic disorder in homozygous recessives that often causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?
f(A1) = 0.9700, f(A2) = 0.0300
When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of _____.
frequency-dependent selection
The following question is based on information in Hopi E. Hoekstra, Kristen E. Drumm, and Michael W. Nachman, "Ecological Genetics of Adaptive Color Polymorphism in Pocket Mice: Geographic Variation in Selected and Neutral Genes," Evolution 58(6), 2004: 1329-41.
Allele change for the neutral mitochondrial genes serves as a control and gives information on any general background genetic difference among these populations.
The higher the proportion of loci that are "fixed" in a population, the lower that population's _____.
nucleotide variability and average heterozygosity
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?
0.81
Genetic variation _____.
must be present in a population before natural selection can act upon the population
Suppose 64% of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg expectations for this gene, what percentage of the population must be heterozygous for this trait?
48%
In some jacana species, males take care of the eggs and young, and females compete among themselves for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements would you predict to be true of this bird species?1. Male jacana fitness is primarily limited by ability to take care of eggs and raise young.2. Female jacana fitness is limited by the number of males in her territory with which a female mates.3. Variation in reproductive success should be greater in male jacanas than in females.4. Variation in reproductive success should be greater in female jacanas than in males.5. Males and females have equal variation in reproductive success.
1, 2, and 4
A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?
disruptive selection
Researchers studying a small milkweed population note that some plants produce a toxin and other plants do not. They identify the gene responsible for toxin production. The dominant allele (T) codes for an enzyme that makes the toxin, and the recessive allele (t) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The genotypes of all individuals in the population are determined to be f(TT) = 0.56, f(Tt) = 0.28, and f(tt) = 0.16. Find the allele frequencies f(T) and f(t) and use them to decide whether the population is in Hardy-Weinberg equilibrium (HWE) or not.
No, the population is not in HWE, because there are more homozygotes than expected.
The figure above shows the distribution of pocket-mouse coat colors in several Arizona populations found either on light-colored granite substrate or on dark volcanic rock (dark substrate). The Melanocortin-1 receptor (Mc1r) alleles, D and d, differ by four amino acids. Mice with DDand Dd genotypes have dark coats, whereas mice with the ddgenotype are light colored. What sort of genotype frequencies might you expect to find in the Xmas, Mid, and O'Neill populations?
Xmas-high dd frequency; Mid-high DD frequency, O'Neill-high Ddfrequency
A large population of laboratory animals has been allowed to breed without human interference 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.Assuming the population is in Hardy-Weinberg equilibrium, what proportion of the population is expected to be heterozygous (Aa) for this trait?
0.5
The fact that organisms cannot necessarily evolve any trait that could be an advantage reflects _____.
the limits of historical constraints
A large population of laboratory animals has been allowed to breed without human interference 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.Assuming the population is in Hardy-Weinberg equilibrium, what is the estimated frequency of allele A in the gene pool?
0.5
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 intron2. substitution mutation at the third position of an exonic codon3. substitution mutation at the second position of an exonic codon4. deletion mutation within the first exon of the gene
4, 3, 2, 1
In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because _____.
heterozygotes can come about in two ways
Which of the following is a fitness trade-off (compromise)?
Turtle shells provide protection from predators but are heavy and burdensome when moving.
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?
average heterozygosity
Which statement about variation is true?
All new alleles are the result of nucleotide variability.
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 (survival rate) 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 _____.
cross your flies with flies from another lab
In 1983 a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.)The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to _____.
a founder effect
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. The outcome of the conflict between bacteria and bacteriophage at any point in time results from _____.
frequency-dependent selection
Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?
disruptive selection
Refer to the figure above. In their investigation of natural selection on Mc1r alleles (the gene that determines coat color) in Arizona pocket mice, Hoekstra et al. determined the frequency of the D and d alleles in each population. They also determined the frequency of alleles for two neutral mitochondrial DNA genes (genes that do not affect and are not linked to coat color). Why did the researchers include the mitochondrial DNA genes as part of their experimental design?
Allele change for the neutral mitochondrial genes serves as a control and gives information on any general background genetic difference among these populations.
Which of the following is the best modern definition of evolution?
descent with modification
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 (survival rate) 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 _____.
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