Chapter 23 Bio

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 founder event a genetic bottleneck disruptive selection directional selection

a genetic bottleneck

Genetic drift produces variation for evolution when ________. a population has heritable traits better suited to the environment a gene pool decreases because a smaller group establishes a new population chance events cause allele frequencies to fluctuate unpredictably sudden change in environment drastically reduces the gene pool

chance events cause allele frequencies to fluctuate unpredictably

Microevolutions occur when ________. gene flow evenly transfers alleles between populations a bird has a beak of a particular size that does not grow larger during a drought individuals within all species vary in their phenotypic traits changes in allele frequencies in a population occur over generations

changes in allele frequencies in a population occur over generations

Which of the following is the most predictable outcome of increased gene flow between two populations? lower average fitness in both populations increased genetic difference between the two populations higher average fitness in both populations decreased genetic difference between the two populations

decreased genetic difference between the two populations

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 _____. neutral variation stabilizing selection genetic drift disruptive selection directional selection

directional selection

Use the following information to answer the question below.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 it is present in African-Americans whose ancestors were from equatorial Africa. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa? disruptive selection; stabilizing selection directional selection; disruptive selection stabilizing selection; disruptive selection directional selection; stabilizing selection

directional selection; stabilizing selection

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? stabilizing selection disruptive selection genetic drift directional selection

disruptive 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 directional selection stabilizing selection sexual selection

disruptive selection

Cystic fibrosis is a genetic disorder in homozygous recessives that 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 equation? f(A1) = 0.9800, f(A2) = 0.0200 f(A1) = 0.9604, f(A2) = 0.0392 f(A1) = 0.9700, f(A2) = 0.0300 f(A1) = 0.9997, f(A2) = 0.0003

f(A1) = 0.9700, f(A2) = 0.0300

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

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 neutral variation heterozygote advantage evolutionary imbalance

frequency-dependent selection

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 _____. balancing selection frequency-dependent selection sexual selection stabilizing selection

frequency-dependent selection

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus? Without more information, gene variability and number of alleles cannot be determined. gene variability > 0%; number of alleles = 2 gene variability = 0%; number of alleles = 0 gene variability = 0%; number of alleles = 1 gene variability = 0%; number of alleles = 2

gene variability = 0%; number of alleles = 1

One of the following is NOT a source of genetic variation. alteration of gene number or position rapid reproduction mutation sexual reproduction genetic drift

genetic drift

Which Hardy-Weinberg condition is affected by population size?selection genetic drift gene flow no mutation

genetic drift

On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences.If one builds a canal linking a predator-rich pond to a predator-poor pond, then what type of selection should subsequently be most expected among the mosquitofish in the original predator-rich pond, and what type should be most expected among the mosquitofish in the formerly predator-poor pond? less-intense directional selection; more-intense directional selection stabilizing selection; stabilizing selection less-intense disruptive selection; more-intense disruptive selection stabilizing selection; directional selection

less-intense directional selection; more intense directional selection

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

microevolution

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 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 in many cases, phenotype is determined by genotype and the environment 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

If individuals tend to mate within a subset of the population, there is ________. no gene flow no genetic drift no selection no random mating

no random mating

Pseudogenes are _____. composed of RNA, rather than DNA nonfunctional vestigial genes the same things as introns unrelated genes that code for the same gene product

nonfunctional vestigial genes

The higher the proportion of loci that are "fixed" in a population, the lower are that population's ________. nucleotide variability and average heterozygosity chromosome number nucleotide variability average heterozygosity

nucleotide variability and average heterozygosity

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

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. sexual selection genetic drift immigration sexual reproduction mutation

sexual reproduction

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 0.9 0.49 0.09

0.09

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 0.50 0.25 0.05

0.50

Use the following information to answer the question(s) below.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? 0.125 0.75 0.25 0.50

0.50

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

All new alleles are the result of nucleotide variability.

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? 0.08 0.09 0.70 Allele frequency cannot be determined from this information.

Allele frequency cannot be determined from this information.

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? Disruptive selection Directional selection Stabilizing selection

Directional Selection

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

Disruptive 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

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? 0.64 0.80 0.36 0.75

.80

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 increase in frequency. 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, 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 fosters the exchange of genes between different populations. 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 restricts the gene pool by chance events such as floods or other catastrophic events.

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

What is true of microevolution? 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 is restricted to individual organisms. It is evolution that influences only a small subset of the populations that comprise a species. It is evolution that results in the origin of small numbers of new 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 the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations.

What must be true of any organ described as vestigial? It must be homologous to some feature in an ancestor. It must be analogous to some feature in an ancestor .It need be neither homologous nor analogous to some feature in an ancestor. It must be both homologous and analogous to some feature in an ancestor.

It must be homologous to some feature in an ancestor.

Members of two different species possess a similar-looking structure that they use in a similar way to perform about the same function. Which of the following would suggest that the relationship more likely represents homology instead of convergent evolution? The structures in adult members of both species are similar in size. Both species are well adapted to their particular environments. The two species share many proteins. The two species live at great distance from each other.

The two species share many proteins.

HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.Which mechanism produces variation for evolution by shuffling existing alleles? rapid reproduction mutation sexual reproduction changes in chromosome numbers

sexual reproduction

Which one of the following conditions would allow gene frequencies to change by chance? mutation gene flow large population small populations

small populations

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? directional selection sexual selection stabilizing selection disruptive selection

stabilizing selection

Which one of these processes describes bottleneck effect? alleles transferred to the next generation in portions that differ from previous generation transfer of alleles in and out of a population due to movement of fertile individuals chance events that change allele frequency sudden change in environments that alters gene frequency of a population

sudden change in environments that alters gene frequency of a population

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, _____. natural selection, gene flow, and genetic drift are acting equally to change an allele's frequency individuals within the population are evolving the allele's frequency should not change from one generation to the next two alleles are present in equal proportions

the allele's frequency should not change from one generation to the next