22. Evolution of Populations

The human genome consists of approximately 3 billion base pairs. If humans typically differ from one another by about 3 million base pairs, what is the nucleotide variability of Homo sapiens?

Stabilizing selection __________.

Which of the following mechanisms can form entirely new alleles?

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

Which of the following would seem to be an example of neutral variation?

What is the importance of neutral variation in evolution?

__________ and __________ generate variation, whereas __________ results in an adaptation to the environment.

A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown, and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to __________.

An earthquake hits a small island. All but a small group of closely related lizards are eliminated, and the survivors spread out over the island. This is an instance of __________.

Which of the following scenarios would most likely result in the microevolution of a population of humans?

Which of the following is the best example of gene flow?

Which of the following most accurately measures an organism's fitness?

The lethal genetic disorder Tay-Sachs disease occurs in individuals with two copies of a recessive allele of the responsible gene. Which of the following statements is true?

Antibiotic resistance in bacteria is an example of which of the following?

For several years, scientists have warned doctors of the danger of overprescribing antibiotics such as penicillin. Scientists are concerned because __________.

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

Birds with average-size wings survived a severe storm more successfully than other birds in the same population with longer or shorter wings. If severe storms occur regularly, then over time, one should expect these storms to bring about __________.

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

Selection that acts over evolutionary time to preserve traits that increase an individual's ability to mate is known as __________.

Which statement below is true about sexual selection?

A number of mosquito populations today are resistant to insecticides that were once quite effective. Biologists think that insecticide resistance evolved in mosquitoes because __________.

Natural selection changes allele frequencies because some _________ survive and reproduce better than others. a. alleles b. loci c. species d. individuals

The largest unit within which gene flow can readily occur is a a. population. b. species. c. genus. d. hybrid.

How do the phospholipids in archaea differ from those in other cells? a. They have tails made of unsaturated fatty acids instead of saturated fatty acids. b. They do not contain hydrocarbon chains. c. They have isoprenoid tails instead of fatty acid tails. d. They have two hydrocarbon chains instead of three hydrocarbon chains.

What two functional groups are bound to the central carbon of every free amino acid monomer? a. an R-group and a hydroxyl group b. an N—H group and a ═(C═O) group c. an amino group and a hydroxyl group d. an amino group and a carboxyl group

No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is a. new mutations that occurred in the preceding generation. b. genetic drift. c. the reshuffling of alleles in sexual reproduction. d. environmental effects.

Why isn't inbreeding considered an evolutionary process? a. It does not change genotype frequencies. b. It does not change allele frequencies. c. It does not occur often enough to be important in evolution. d. It does not violate the assumptions of the Hardy–Weinberg principle.

Describe three ways that evolution can occur via genetic drift.

Why is genetic drift aptly named? Select True or False for each statement. T/F It causes allele frequencies to drift up or down randomly. T/F It occurs when alleles from one population drift into another. T/F It occurs when mutations drift into a genome.

Which of these functional groups is known to be used for storing large amounts of chemical energy? a. amino group b. carbonyl group c. phosphate group d. sulfhydryl group

Evaluate the following statements related to the synthesis of nucleic acids. Select True or False for each statement. T/F Ribonucleotides are added to the 3′ end of a DNA strand. T/F Polymerization of nucleic acids occurs by the formation of phosphodiester bonds. T/F Complementary pairing between sugars is required for copying nucleic acids. T/F Strands in a double helix are synthesized in an antiparallel orientation.

Evaluate this statement: Gene flow increases the genetic divergence of populations.

True or false? Gene flow can either increase or decrease the average fitness of a population. Explain.

Add labels to the figure that follows, which illustrates how Mycobacterium tuberculosis evolves when it is exposed to an antibiotic.

What is responsible for the increased stability of DNA compared to RNA?

Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Describe, on a molecular level, how you would expect these lipids to behave in water.

In an area of erratic rainfall, a biologist found that grass plants with alleles for curled leaves reproduced better in dry years, and plants with alleles for flat leaves reproduced better in wet years. This situation would tend to _________ . (Explain your answer.) a. cause genetic drift in the grass population. b. preserve genetic variation in the grass population. c. lead to stabilizing selection in the grass population. d. lead to uniformity in the grass population.

If nucleotides from the DNA of a human were quantified and 30 percent of them contained the base adenine, what percentage of them would contain the base guanine? a. 20 percent b. 30 percent c. 40 percent d. 70 percent

If an allele is recessive and lethal in homozygotes before they reproduce, a. the allele will be removed from the population by natural selection in approximately 1,000 years. b. the allele will likely remain in the population at a low frequency because it cannot be selected against in heterozygotes. c. the fitness of the homozygous recessive genotype is 0. d. both b and c are correct.

In the 1700s and 1800s, royalty in Europe often married their close relatives; furthermore, recessive genetic diseases such as hemophilia showed up much more often among royals than in the general population. Explain the likely connection.

The heritable differences among organisms are a result of                   . a. differences in their DNA; b. mutation; c. differences in alleles; d. A and B are correct; e. A, B, and C are correct

What would be the sequence of the strand of DNA that is made from the following template: 5′-GATATCGAT-3′? (Your answer must be written 5'→3'.) How would the sequence be different if RNA were made from this DNA template?

According to the RNA world model, a ribozyme would replicate by creating a double-stranded RNA intermediate. Would you expect the intermediate to have the same catalytic activity as the original ribozyme? Justify your answer with an explanation.

A new plant species C, which formed from hybridization of species A(2n = 16) with species B(2n = 12), would probably produce gametes with a chromosome number of a. 12. b. 14. c. 16. d. 28.

Draw a small concept map showing how selection, genetic drift, gene flow, and mutation relate to genetic variation.

The risks faced by small populations include                   . a. erosion of genetic variability through genetic drift; b. decreased fitness of individuals as a result of inbreeding; c. increased risk of experiencing natural disasters; d. A and B are correct; e. A, B, and C are correct

Ivory from elephant tusks is a valuable commodity on the world market. As a result, male African elephants with large tusks have been heavily hunted for the past few centuries. Today, male elephants have significantly shorter tusks at full adulthood than male elephants in the early 1900s. This is an example of                   . a. diversifying selection; b. stabilizing selection; c. directional selection; d. chance; e. more than one of the above is correct

A horse (2n = 64) and a donkey (2n = 62) can mate and produce a mule. How many chromosomes would there be in a mule's body cells? a. 31 b. 62 c. 63 d. 126

Antibiotic resistance is becoming common among organisms that cause a variety of human diseases. All of the following strategies help reduce the risk of antibiotic resistance evolving in a susceptible bacterial population except                   . a. using antibiotics only when appropriate, for bacterial infections that are not clearing up naturally; b. using the drugs as directed, taking all the antibiotic over the course of days prescribed; c. using more than one antibiotic at a time for difficult-to-treat organisms; d. preventing natural selection by reducing the amount of evolution the organisms can perform; e. reducing the use of antibiotics in non–health-care settings, such as agriculture

Suppose you were studying several species of monkeys. In one, males never helped females raise offspring. In another, males provided just as much parental care as females except for actually carrying the fetus during pregnancy. How does the fundamental asymmetry of sex compare in the two species? How would you expect sexual dimorphism to compare between the two species?

Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest? Toucans disperse seeds of key forest species such as juçara palms by eating the fruit and defecating the seeds in new locations, sometimes more than a kilometer away. If there are no toucans, is the genetic diversity of palms likely to increase or decrease within forest fragments? Why? a. increase (due to increased genetic drift) b. decrease (due to decreased gene flow) c. decrease (due to decreased mutation rate) d. decrease (due to decreased natural selection)

Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest? Toucans can eat fruits with large seeds because their large bills can open wide. Most other birds in the same forest can only eat small seeds. Ecologist Mauro Galetti and his colleagues measured the seed sizes of palms in forest fragments with and without toucans. The graphs show two of the forest populations they studied. What is the take-home message of the data?

It seems logical that natural selection would work toward genetic uniformity; the genotypes that are most fit produce the most offspring, increasing the frequency of adaptive alleles and eliminating less adaptive alleles. Yet there remains a great deal of genetic variation within populations. Describe factors that contribute to this variation.