Chapter 23 Homework

Part A Which of the following is a fitness trade-off (compromise)?

Turtle shells provide protection but are heavy and burdensome when moving

Part A 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

Part A In evolutionary terms, an organism's fitness is measured by its _____.

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.

Part A Which of the following is the most predictable outcome of increased gene flow between two populations?

decreased genetic difference between the two populations

Part A In a very large population, a quantitative trait has the following distribution pattern. If there is no gene flow, the curve shifts to the left or to the right, and the population size consequently increases over successive generations, which of the following is most likely occurring?

directional selection

Part A Mutation is the only evolutionary mechanism that _____.

does little to change allele frequencies

Part A Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.

gene flow

Part A Click on the diagram to start the animation. What process is illustrated by this animation?

gene flow Gene flow is the migration of individuals or gametes.

Part A The evolutionary effects of genetic drift are greatest when _____.

he population size is small Changes in the gene pool of a small population are frequently due to genetic drift.

Natural selection changes allele frequencies because some _______ survive and reproduce more successfully than others.

individuals

Part A Use the following description to answer the question(s) below. 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(s) of selection should subsequently be most expected among the mosquitofish in the original predator-rich pond, and what type(s) should be most expected among the mosquitofish in the formerly predator-poor pond?

less-intense directional selection; more-intense directional selection

Part C Generation-to-generation change in the allele frequencies in a population is _____.

microevolution Generation-to-generation change in the allele frequencies in a population is the definition of microevolution.

Genetic variation _____.

must be present in a population before natural selection can act upon the population

The original source of all genetic variation is _____.

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.

Part B Click on the diagram to start the animation. What process is illustrated by this animation?

natural selection This is natural selection, since environmental conditions dictate that green individuals are more likely to reproduce than are red individuals.

Part A 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

Part A For a biologist studying a small fish population in the lab, which Hardy-Weinberg condition is easiest to meet?

no gene flow

Part B You are a researcher working closely with the Leakey family, studying the newly discovered fossils to determine their place in the human lineage. Which of the following are you?

paleoanthropologist

Part D Which of the following is the closest relative to Homo sapiens?

the orangutan, a great ape

Part A No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is

the reshuffling of alleles in sexual reproduction.

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

Part A 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?

0.50

Part A 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

Part C You are a reproductive biologist interested in the mating behavior of dogs. How many times a year can you study the Carolina dog?

1

Part A 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.

Part A Different finch species have beaks of different shapes and sizes. What do these beak differences tell us?

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."

Part A Which of the following is currently thought to be true?

Dogs arrived in North America before European colonization.

Part A 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.

Part B - Determining the expected frequency of each genotype Considering the same population of cats as in Part A, what is the expected frequency of each genotype (TLTL, TLTS, TSTS ) based on the equation for Hardy-Weinberg equilibrium? Keep in mind that you just learned in Part A that: The allele frequency of TL is 0.4. The allele frequency of TS is 0.6. The equation for Hardy-Weinberg equilibrium states that at a locus with two alleles, as in this cat population, the three genotypes will occur in specific proportions: p2+2pq+q2=1 Enter the values for the expected frequency of each genotype: TLTL, TLTS, and TSTS. Enter your answers numerically to two decimal places, not as percentages. For help applying the Hardy-Weinberg equation to this cat population, see Hints 1 and 2.

The TL allele accounts for 160 of the alleles (60 × 2 = 120 in TLTL cats, plus 40 × 1 = 40 in TLTS cats). Therefore, the TL allele makes up 40% (160/400) of the alleles in the population, so the value of p is 0.4. The allele frequencies of the population must add up to one (in other words, p+q=1); therefore, since the value of p is 0.4, the value of q is 0.6. According to the Hardy-Weinberg equation, the expected frequencies of the genotypes should add up to 1. p2+2pq+q2=1 0.42+2(0.4)(0.6)+0.62=1 0.16+0.48+0.36=1

Part A Which of the following specimens discovered in 1972 ignited the debate about multiple lineages within the genus Homo?

1470

Part A 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%

Part A If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be _____.

54%

Using the Hardy-Weinberg equation to determine if a population appears to be evolving A hypothetical population of 300 wolves has two alleles, FB and FW, for a locus that codes for fur color. The table below describes the phenotype of a wolf with each possible genotype, as well as the number of individuals in the population with each genotype. Which statements accurately describe the population of wolves? Genotype Phenotype (fur color) Number of individuals in population FBFB black 40 FBFW gray 40 FWFW white 220 Select the four statements that are true.

Based on the equation for Hardy-Weinberg equilibrium, the expected number of wolves with the FBFB genotype is 12. Based on the equation for Hardy-Weinberg equilibrium, the expected number of wolves with the FBFW genotype is 96. The population may be evolving because the actual number of individuals with each genotype differs from the expected number of individuals with each genotype. The population is not at Hardy-Weinberg equilibrium. The FB allele accounts for 120 of the alleles (40 × 2 = 80 in FBFB wolves, plus 40 × 1 = 40 in FBFW wolves). Therefore, the FB allele makes up 20% (120/600) of the alleles in the population, so the value of p is 0.2. The allele frequencies of the population must add up to one (in other words, p+q=1); therefore, since the value of p is 0.2, the value of q is 0.8. According to the Hardy-Weinberg equation, the expected frequencies of the genotypes should add up to 1. p2+2pq+q2=1 0.22+2(0.2)(0.8)+0.82=1 0.04+0.32+0.64=1 To predict the number of individuals with each genotype, multiply the expected frequency of each genotype by the number of individuals in the population. 0.04×300=12 FBFB individuals 0.32×300=96 FBFW individuals 0.64×300=192 FWFW individuals The wolf population may be evolving because the expected number of individuals with each genotype, calculated with the Hardy-Weinberg equation, does not equal the actual number of individuals with each genotype.

You are interested in adopting a dog and want it to be an ancient breed. Which of the following should you pick?

Basenji

Part E The Grants witnessed strong selection during droughts in 1977 and 1985. Compare the two droughts. Select all that apply.

Both droughts events provided strong natural selection on medium ground finch populations 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 the1977 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.

The Hardy-Weinberg Principle The Hardy-Weinberg principle states that, if a population is not evolving, then the frequencies of alleles and genotypes in that population will remain constant from one generation to the next. Further, this principle allows us to predict what the genotype frequencies will be in a non-evolving population. We can conclude that a population may be evolving if its genotype frequencies differ from those predicted by the Hardy-Weinberg principle. Part A - Analyzing the gene pool of a hypothetical population A hypothetical population of 200 cats has two alleles, TL and TS, for a locus that codes for tail length. The table below describes the phenotypes of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Which statements about the population are true?

Heterozygotes make up 20% of the population. Homozygotes make up 80% of the population. In the entire cat population, 60% of the alleles are TS. In the entire cat population, the frequency of the TL allele is 0.4. Assuming random mating, each gamete has a 40% chance of having a TL allele and a 60% chance of having a TS allele. The gene pool for tail length in the population is composed of alleles TL and TS . The allele frequency of TL is 0.4 (160/400). Another way to express this is that 40% of the alleles are TL . The allele frequency of Ts is 0.6 (240/400). Another way to express this is that 60% of the alleles are Ts . Therefore, each gamete (sperm or egg) has a 40% chance of carrying allele TL and a 60% chance of carrying allele Ts , assuming mating is random.

Part C You discover the skull of a species very similar to 1470. Which of the following two species is it most like?

Homo habilis and Homo rudolfensis

Part E Which of the following do most biologists currently think is true?

Human evolution followed a path with many branches.

Part E You are a zoologist studying hunting behavior of predators in the wild. What should you expect when observing Carolina dogs?

Hunting as a pack.

Part G The film defines species as populations whose members don't interbreed. What keeps different Galápagos finch species from mating? Select all that apply.

Individuals recognize and only respond to songs of their own species. Males only court females that have a similar beak and similar size. Geographic isolation and different environments led to changes in traits that affected mating. Correct 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.

Part B You find a stray dog while out walking. Which of the following would convince you that it is a Carolina dog?

It has a fishhook tail and it digs snout pits.

Part B Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos islands?

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.

Part A The following experiment is used for the corresponding question. A researcher discovered a species of moth that lays its eggs on oak trees. Eggs are laid at two distinct times of the year: early in spring when the oak trees are flowering and in midsummer when flowering is past. Caterpillars from eggs that hatch in spring feed on oak flowers and look like oak flowers. But caterpillars that hatch in summer feed on oak leaves and look like oak twigs. How does the same population of moths produce such different-looking caterpillars on the same trees? To answer this question, the biologist caught many female moths from the same population and collected their eggs. He put at least one egg from each female into eight identical cups. The eggs hatched, and at least two larvae from each female were maintained in one of the four temperature and light conditions listed below. In each of the four environments, one of the caterpillars was fed oak flowers, the other oak leaves. Thus, there were a total of eight treatment groups (4 environments × 2 diets). Refer to the accompanying figure. Recall that eggs from the same female were exposed to each of the eight treatments used. This aspect of the experimental design tested which of the following hypotheses?

The differences are genetic. A female will either produce all flowerlike caterpillars or all twig-like caterpillars.

Part C Bar graph shows a histogram with columns representing numbers of birds with different sized beaks. Before the drought, the majority of individuals have beak depths between 8.8 mm and 9.8 mm. The majority of the much smaller population of drought survivors has beak depths between 9.8 and 10.3 mm. In 1977, medium ground finches on Daphne Major experienced a severe drought. The figure shows the beak depths of the initial population before the drought (red bars) and of the drought survivors (black bars). What do the data show? Select all that apply.

The most common beak size of the initial population was 8.8 millimeters. A very small proportion (~5%) of the initial population with this beak size survived. Finches with larger beaks had a survival advantage in the 1977 drought. More than one-half of the initial population died during the drought. Most of the survivors of the 1977 drought had larger beaks. When small seeds became scarce in the drought, more medium ground finches with smaller beaks ran out of food and died. Finches with larger beaks were better able eat the larger, harder seeds.

Part D The top figure shows beak sizes of the 1976 finch population before the drought of 1977 (red bars) and after the drought (black bars). The lower figure shows the beak sizes of the offspring of the drought survivors in 1978. What do these figures tell us?

The overall beak depths of the 1978 offspring population are larger the original 1976 population. Correct As mentioned in the film, the average beak depth of the population increased by more than 4% in just one generation.

Part A 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 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.

Part F How did the Grants test their hypothesis that differences in birds' songs can keep different species of finches from breeding with one another?

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.

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