Mastering Bio Ch 23

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? a) Directional selection b) Stabilizing selection c) Disruptive selection

a) Directional selection Directional selection drives the average of the population in one direction, in this case, toward longer necks.

How does Dr. Allison's work provide an example of natural selection in humans? Select all that apply. a) In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles. b) In areas with malaria, natural selection causes individuals to acquire the sickle cell allele as protection against malaria. c) Natural selection caused the sickle cell allele to appear in east African populations. d) In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease.

a) In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles. d) In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease. In different environments, natural selection favors different characteristics. In areas with malaria, the reproductive advantages of having one sickle cell allele (and some protection from malaria) kept the allele at high frequencies in the population. In areas without malaria, the reproductive disadvantages from sickle cell disease reduced the allele in populations.

The film defines species as populations whose members don't interbreed. What keeps different Galápagos finch species from mating? Select all that apply. a) Individuals recognize and only respond to songs of their own species. b) Males only court females that have a similar beak and similar size. c) One population eats mostly small, soft seeds and the other population eats mostly large, hard seeds. d) Geographic isolation and different environments led to changes in traits that affected mating.

a) Individuals recognize and only respond to songs of their own species. b) Males only court females that have a similar beak and similar size. d) Geographic isolation and different environments led to changes in traits that affected mating. The Grants and their team gathered evidence to show that finches choose mates on the basis of song and appearance. Changes in behavior can help create reproductive isolation, which keeps species from mating.

In some populations, 1 in 500 people have sickle cell disease. What reason does the film give for why a potentially deadly, inherited disease is found at such high frequencies? a) Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population. b) Individuals with two sickle cell alleles have an evolutionary advantage because they do not get sickle cell disease or get infected with malaria. c) Individuals with two normal hemoglobin alleles get both sickle cell disease and are susceptible to malaria, so these alleles are eliminated from the population. d) Sickle cell alleles are new mutations and not enough time has gone by for these alleles to be eliminated from the population by natural selection.

a) Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population. People with one sickle cell allele are protected from malaria, but do not have sickle cell disease. Protection from malaria comes at the cost of more sickle cell disease in the population.

Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards? a) Stabilizing selection b) Directional selection c) Disruptive selection

a) Stabilizing selection Stabilizing selection causes no change in the average of the population; extreme phenotypes (large and small lizards) become less common.

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? a) The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread. b) Resistance to DDT evolved in some fruit flies in order to allow them to survive. c) Alleles for DDT resistance arose by mutation during the period of DDT use because of selection for pesticide resistance.

a) 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.

In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following? a) The value of a particular characteristic; characteristics of an organism can include such traits as size and color. b) Time c) The number of individuals

a) The value of a particular characteristic; characteristics of an organism can include such traits as size and color. The value of the characteristic increases from left to right.

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 _____. 23.4 (Page 495) a) directional selection b) neutral variation c) disruptive selection d) genetic drift e) stabilizing selection

a) directional selection The characteristics of the poppies shifted in response to the changed environment.

There are 40 individuals in population 1, all with genotype A1A1, and there are 25 individuals in population 2, all with genotype A2A2. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of a) genetic drift. b) disruptive selection. c) gene flow. d) directional selection. e) discrete variation.

a) genetic drift.

Natural selection changes allele frequencies because some _______ survive and reproduce more successfully than others. a) individuals b) alleles c) species d) gene pools e) loci

a) individuals

The original source of all genetic variation is _____. 23.1 (Page 485) a) mutation b) independent assortment c) sexual reproduction d) natural selection e) recombination

a) mutation Mutation is, in itself, very important to evolution because it is the original source of the genetic variation that serves as the raw material for evolution.

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) 0.49 b) 0.09 c) 0.9 d) 9.0

b) 0.09

The Grants witnessed strong selection during droughts in 1977 and 1985. Compare the two droughts. Select all that apply. a) In both droughts, large-beaked medium ground finches had the highest survival rates. b) Both droughts events provided strong natural selection on medium ground finch populations. c) In both droughts, small-beaked medium ground finches had the highest survival rates. d) Both droughts resulted in changes to food sources that favored the survival of some medium ground finches over others.

b) Both droughts events provided strong natural selection on medium ground finch populations. d) Both droughts resulted in changes to food sources that favored the survival of some medium ground finches over others. Natural selection simply favors the characteristics that are best in a particular situation. If the situation changes, natural selection favors different characteristics. The primary food source after the 1977 drought was large, hard seeds, which favored large-beaked birds. The primary food source after the 1985 drought was small seeds, which favored small-beaked birds.

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers? a) Stabilizing selection b) Disruptive selection c) Directional selection

b) Disruptive selection Disruptive selection causes both extreme phenotypes (large and small beaks) to be favored over the intermediate phenotypes.

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. a) True b) False

b) False Heterozygote advantage results in more genetic variation in the population.

Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos islands? a) The 13 species have existed on the Galápagos islands since the islands first formed. b) Many years ago, a small population of a single finch species migrated to the islands and evolved into the current 13 species. c) Many years ago, more than 13 different species of birds migrated to the islands. The current 13 finch species are the only species that survived. d) Each of the 13 species migrated to the islands at different times over the years.

b) Many years ago, a small population of a single finch species migrated to the islands and evolved into the current 13 species. The Galápagos finch DNA reveals that the finch species are more related to each other than to any species on the mainland.

Compare sickle cell disease and malaria. a) Sickle cell disease and malaria are both genetic diseases. b) Sickle cell disease and malaria are both potentially lethal diseases. c) Sickle cell disease and malaria are both infectious diseases. d) Sickle cell disease and malaria are both inherited diseases.

b) Sickle cell disease and malaria are both potentially lethal diseases. Though malaria is an infectious disease and sickle cell disease is inherited, both can cause life-threatening conditions.

Which statement correctly describes the role of chance in evolution? a) An allele that increases evolutionary fitness cannot be lost from a population by chance events. b) The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA. c) Evolution by natural selection proceeds by an accumulation of changes that occur by chance.

b) The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA. Genetic variation does arise by chance mutations.

One out of 10,000 babies born in North America is affected by cystic fibrosis, a recessive condition. Assuming that the North American human population is in Hardy-Weinberg equilibrium for this trait, what percentage of the population is heterozygous for this trait? (Remember the equation for a population in Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1.) a) 0.01% b) 1% c) 2%

c) 2% If the trait is in Hardy-Weinberg equilibrium, then its frequency is not changing in the population from generation to the next.

Which type of selection tends to increase genetic variation? a) Stabilizing selection b) Directional selection c) Disruptive selection

c) Disruptive selection Disruptive selection eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population.

How did Dr. Allison test his hypothesis that sickle cell disease was connected to malaria? Select all that apply. a) He looked for the underlying genetic mechanism causing sickle cell disease. b) He studied the way that the malaria parasite interacts with sickle cells. c) He evaluated blood samples for malaria parasites and the presence of sickle cells. d) He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected.

c) He evaluated blood samples for malaria parasites and the presence of sickle cells. d) He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected. Dr. Allison gathered blood samples from more than 5,000 children in East Africa. He analyzed the samples to identify malaria parasites and sickle cells. He found that children carrying the sickle cell character (or trait) had a lower parasite count, as if they were partially protected against malaria.

In 1949, Dr. Tony Allison observed a high frequency of Kenyans carrying the sickle cell allele in coastal areas and near Lake Victoria, but a lower frequency in the highlands. What did he hypothesize? a) He hypothesized that malaria is a genetic disease. b) He hypothesized that sickle cell disease was an environmental, not a genetic disease. c) He hypothesized that there was a connection between malaria and sickle cell disease. d) He hypothesized that malaria causes sickle cell disease.

c) He hypothesized that there was a connection between malaria and sickle cell disease. On the basis of this hypothesis, Dr. Allison predicted high frequencies of sickle cell disease only in areas where malaria is common.

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies? a) Disruptive selection b) Directional selection c) Stabilizing selection

c) Stabilizing selection Stabilizing selection causes no change in the average of the population; extreme phenotypes (in this case, large and small babies) become less common.

If a person has two normal copies of the hemoglobin allele, which statements are true? Select all that apply. a) The person is heterozygous at the hemoglobin locus. b) The person is protected against malaria. c) The person is susceptible to malaria. d) The person is homozygous at the hemoglobin locus.

c) The person is susceptible to malaria. d) The person is homozygous at the hemoglobin locus. A person with two copies of any allele is homozygous. A person with two normal copies of the hemoglobin allele is more susceptible to malaria than someone with a sickle cell hemoglobin allele.

Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated. a) The sickle cell allele will increase in frequency. b) The sickle cell allele frequency will not be affected. c) The sickle cell allele will decrease in frequency.

c) The sickle cell allele will decrease in frequency. Without malaria, selection for the sickle cell allele decreases. As a result, the frequency will likely decrease.

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? a) f(A1) = 0.9800, f(A2) = 0.0200 b) f(A1) = 0.9604, f(A2) = 0.0392 c) f(A1) = 0.9700, f(A2) = 0.0300 d) f(A1) = 0.9997, f(A2) = 0.0003

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

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

c) gene variability = 0%; number of alleles = 1

Which Hardy-Weinberg condition is affected by population size? a) gene flow b) selection c) genetic drift d) no mutation

c) genetic drift

Different finch species have beaks of different shapes and sizes. What do these beak differences tell us? a) Different finch beak shapes are evidence that all Galápagos finches share a common ancestor. b) Different finch beak shapes are evidence that several finch species with different beak types came to the Galápagos Islands from the mainland. c) Different finch beak shapes are evidence that individual birds changed their beaks so that they could feed efficiently. d) Different finch beak shapes are evidence that finch species adapted to different environments over many generations.

d) Different finch beak shapes are evidence that finch species adapted to different environments over many generations. Having the correct beak shape for a particular food source is important for survival. As Rosemary Grant says, "Beaks are tools and you need the right tool for the right job."

How does diploidy help to preserve genetic variation? See Concept 23.4 (Page 498) a) It helps individual organisms make a greater contribution to the gene pool of the next generation. b) It allows the frequency of a recessive allele in a population to be predicted under certain conditions. c) It fosters the exchange of genes between different populations. d) It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes. e) It restricts the gene pool by chance events such as floods or other catastrophic events.

d) 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.

What is true of microevolution? 23.1 (Page 484) a) It is evolution that is restricted to individual organisms. b) It is evolution that influences only a small subset of the populations that comprise a species. c) It is evolution that involves only tiny changes to DNA, such as point mutations, producing only small (if any) changes to phenotype. d) 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. e) It is evolution that results in the origin of small numbers of new species.

d) 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. Microevolution is a generation-to-generation change in allele frequency.

How did the Grants test their hypothesis that differences in birds' songs can keep different species of finches from breeding with one another? a) They placed stuffed female finches onto branches to see if males would respond. b) They recorded birds singing on the island of Daphne Major to see which type of song was sung more often by each species. c) They observed which birds were mating with each other and listened for the songs the birds were singing. d) They played the songs of medium ground finches and cactus finches through a loudspeaker to see which species responded to each song.

d) They played the songs of medium ground finches and cactus finches through a loudspeaker to see which species responded to each song. The Grants' experiments using recorded finch songs showed that finch species respond to their own song and not to the song of other species. This is an example of reproductive isolation, which keeps species apart.

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is a) Geographic variation within the population. b) Genetic drift due to the small size of the population. c) Environmental effects. d) New mutations that occurred in the preceding generation. e) The reshuffling of alleles in sexual reproduction.

e) The reshuffling of alleles in sexual reproduction.

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population? 23.3 (Page 492) a) bottleneck effect b) mutation c) nucleotide variability d) gene flow e) founder effect

e) founder effect The founder effect is genetic drift attributable to colonization by a limited number of individuals from a parent population.

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. 23.2 (Page 488) a) genetic drift b) immigration c) sexual selection d) mutation e) sexual reproduction

e) sexual reproduction Sexual reproduction does not change the frequency of alleles in the gene pool.