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Question 1

What is evolution?

Answer 1

Descent with modification; a genetic change in a populartion over time

Question 2

How did people think that species arose and diversified before Charles Darwin published his theory of evolution by natural selection?

Answer 2

Creationism; differential use and disuse of body parts accounted for changes between generations and species diversification.

Question 3

What did Darwin observe that led him to develop his ideas about the origin of species?

Answer 3

As Darwin journeyed in the HMS Beagle, he observed the uniformity of geological processes such as volcanism, earthquakes, and erosion. He collected fossils and observed that each continent had animals that were characteristic and different from those on other continents. On the Galapagos, he observed and collected finches from different islands and noted differences in giant tortoises on different Galapagos Islands. These observations led Darwin to the idea of “descent with modification.”

Question 4

How is artificial selection different from natural selection?

Answer 4

In artificial selection, humans select for the traits they desire in plants or animals. In natural selection, environmental factors favor some traits over others.

Question 5

How did Darwin’s ideas challenge prevailing beliefs about life’s diversity and the status of humans?

Answer 5

Darwin’s ideas challenged prevailing beliefs about life’s diversity by using natural processes to explain how species arise. Darwin saw humans as just another species and rejected the idea that humans were specially created. He thereby demoted humans from an exalted position, putting them on an equal footing with other species competing for resources.

Question 6

What is the modern evolutionary synthesis?

Answer 6

the work of Darwin with a modern understanding of genes, chromosomes, and the origins of variation.

Question 7

What is an adaptation, and how do adaptations become more common within a population?

Answer 7

An adaptation is a characteristic that helps an individual survive and reproduce in its environment. Adaptations become more common within a population when they are heritable and when they increase the odds of survival and reproduction.

Question 8

What is the role of genetic variation in natural selection?

Answer 8

Genetic variation is the raw material that natural selection acts on since genetic variation creates variations in phenotypes, some of which are better suited to the current environment.

Question 9

How can natural selection favor different phenotypes at different times?

Answer 9

Natural selection can favor different phenotypes at different times because environments are always shifting in dramatic or subtle ways.

Question 10

Why doesn’t natural selection produce perfectly adapted organisms?

Answer 10

Natural selection does not produce perfectly adapted organisms because each population’s evolution is constrained by its existing gene pool, which limits the possible allele combinations and may not contain every allele necessary to confront every challenge. Chance events may also wipe out adaptive allele combinations. Genetic illnesses that produce symptoms only after reproductive age also can maintain harmful alleles in a population.

Question 11

What is evolutionary fitness

Answer 11

Evolutionary fitness is measured by reproductive success.

Question 12

What are the five conditions required for Hardy–Weinberg equilibrium

Answer 12

• no mutations;
• random mating;
• no emigration or immigration;
• the population is large enough to eliminate random changes in allele frequencies (genetic drift);
• natural selection does not occur.

Question 13

Why is the concept of Hardy–Weinberg equilibrium important?

Answer 13

The concept of Hardy-Weinberg equilibrium is important because it shows that evolution has the potential to occur at all times; in fact, evolution is probably occurring at all times in all populations.

Question 14

Explain the components and meaning of the equation p2 + 2pq + q2 = 1.

Answer 14

In the Hardy-Weinberg equation, p= the frequency of the dominant allele in a population, q= the frequency of the recessive allele, and pq= the product of p and q. The equation p2 + 2pq + q2 = 1 says that all individuals in a population are homozygous dominant, heterozygous, or homozygous recessive (for a gene with only two alleles). By applying the Hardy-Weinberg equation at different times, it is possible to observe changes in allele frequency and determine whether evolution is occurring.

Question 15

Why doesn’t Hardy–Weinberg equilibrium occur in real populations

Answer 15

Hardy-Weinberg equilibrium does not occur in real populations because the conditions for it are never met in real populations

Question 16

Directional Selection

Answer 16

Directional selection selects against phenotypes at one end of the variation spectrum in a population; the variation in the population shifts in the opposite direction.

Question 17

disruptive selection

Answer 17

In disruptive selection, extreme phenotypes are more fit than the intermediate phenotype; the frequency of the intermediate phenotype decreases in the population.

Question 18

stabilizing selection

Answer 18

In stabilizing selection, both extreme variations of phenotype are selected against; the most common phenotype in the population remains around the median.

Question 19

How can natural selection maintain harmful alleles in a population?

Answer 19

Natural selection can only select against phenotypes. If the dominant phenotype is selected for, heterozygous individuals will retain the recessive allele in the population. Also there are times when the heterozygous condition gives advantages to the individual (e.g., cystic fibrosis carriers are less susceptible to cholera). In these instances a balanced polymorphism is seen in the population.

Question 20

How does sexual selection promote traits that would seem to decrease fitness

Answer 20

Sexual selection selects for extreme phenotypes in one sex, and those extreme variations often place the individual at a disadvantage for survival (e.g., a peacock’s longer tail will make him more visible to predators and slower in escaping). However, since these traits increase fitness by increasing mating success, sexual selection remains an active force in the population.

Question 21

intrasexual selection

Answer 21

Intrasexual selection occurs when members of the same sex compete for mating opportunities with the opposite sex. Intersexual

Question 22

intersexual selection

Answer 22

Intersexual selection occurs between males and females of the same species: one sex chooses a mate of the other sex based on the presence of a characteristic.

Question 23

What are some ways that mutations affect an organism’s phenotype?

Answer 23

Mutations introduce new alleles, which may or may not alter the phenotype of an organism.

Question 24

Under what conditions does a mutation in one organism pass to subsequent generations?

Answer 24

A mutation in one organism passes to subsequent generations if it is a mutation that can be inherited. In sexually reproducing organisms, the mutation must appear in a gamete-producing cell. Mutations in somatic cells will not be passed to the next generation. By contrast, a mutation in an organism that produces asexually will be transmitted to all of its offspring.

Question 25

How does sampling error cause genetic drift?

Answer 25

Sampling error occurs when the selected sample (e.g. the alleles making it to the next generation) does not match the larger original pool. Such chance sampling errors result in a change in the allele frequencies of the population, not as a result of adaptive fitness, but as a result of pure chance.

Question 26

founder effect

Answer 26

a new population is started by a small group of individuals that colonize a new area.

Question 27

population bottleneck

Answer 27

In a population bottleneck, a large and genetically variable population experiences a massive die-off, and only a few individuals survive to continue the population.

Question 28

What is the difference between the founder effect and a population bottleneck

Answer 28

In the founder effect, a new population is started by a small group of individuals that colonize a new area. In a population bottleneck, a large and genetically variable population experiences a massive die-off, and only a few individuals survive to continue the population. Both effects result in populations with restricted variety in their gene pools and are therefore prone to genetic drift.

Question 29

How do nonrandom mating and gene flow disrupt Hardy–Weinberg equilibrium?

Answer 29

Nonrandom mating means that not all individuals have an equal chance of reproducing, and this will shift the equilibrium equation. In gene flow, alleles enter or leave the population; this by its very nature disrupts the allele balance in the population.

Question 30

What hypothesis did Conover and Munch test

Answer 30

The researchers tested the hypothesis that fishing results in population shifts towards fish that are smaller at maturity or that mature more slowly.

Question 31

How is a population reared in a tank different from a population in the “real world”?

Answer 31

In the real world the population would be subject to gene flow as fish entered or left. The artificial population might also be subject to genetic drift.

Question 32

The heritability of a trait ranges from 0 (entirely under environmental control) to 1.0 (100% controlled by genes). In Atlantic silversides, the heritability of body size is about 0.2. How would the results of this experiment differ if heritability of body size were higher? What if it approached 0?

Answer 32

If heritability of body size were higher then the results of the experiment would be even more pronounced with the yellow and blue lines even farther from the random control line. If heritability approached zero then all three lines on the graphs should remain about the same.

Question 33

James Hutton

Answer 33

James Hutton influenced Darwin by suggesting that changes in nature were gradual and uniform (a concept called uniformitarianism).

Question 34

Your boss is a plant breeder who asks you to develop a sweeter variety of apple. How would you use artificial selection to achieve this goal? How might natural selection produce the same result? Which process would occur faster?

Answer 34

Have a group of volunteers taste the apples and categorize them based on sweetness. Take the seeds from the sweetest apples, plant them, and repeat the experiment. Natural selection could mimic this if some animal relied on the apple as a food source, and the animal were more attracted to sweeter apples. The seeds of the sweeter apples might get carried farther away from their parent plants than the less sweet apples, increasing the chance of the seeds of the sweeter apple maturing. Artificial selection would be much faster since scientists could ensure that all seeds from the sweetest trees successfully germinate.

Question 35

How does variation arise in an asexually reproducing population? A sexually reproducing population?

Answer 35

Variation arises in all species through mutations. In sexually reproducing species, variation spreads rapidly as a result of genetic recombination during meiosis.

Question 36

What happens to a population if conditions change and no individuals have the allele combinations required to survive and produce offspring?

Answer 36

The population goes extinct

Question 37

Many articles about the rise of antibiotic-resistant bacteria claim that overuse of antibiotics creates resistant strains. How is this incorrect?

Answer 37

Within populations of bacteria, random mutations are constantly occurring. Exposure to antibiotics does not cause such mutations, but it does cause the death of the bacteria that do not inherit alleles that confer resistance.

Question 38

Explain how harmful recessive alleles can persist in populations, even though they prevent homozygous individuals from reproducing.

Answer 38

Harmful recessive alleles can “hide” behind dominant alleles in the heterozygous condition of balanced polymorphisms, especially if the heterozygote individual carries some advantage (e.g., in sickle cell anemia where individuals resist malaria).

Question 39

Fraggles are mythical, mouselike creatures that live underground beneath a large vegetable garden. Of the 100 Fraggles in this population, 84 have green fur, and 16 have gray fur. A dominant allele F confers green fur, and a recessive allele f confers gray fur. Assuming Hardy–Weinberg equilibrium is operating, answer the following questions. (a) What is the frequency of the gray allele f ? (b) What is the frequency of the green allele F? (c) How many Fraggles are heterozygotes (Ff)? (d) How many Fraggles are homozygous recessive (ff)? (e) How many Fraggles are homozygous dominant (FF)?

Answer 39

(a) The frequency of the gray allele is 0.4. (b) The frequency of the green allele is 0.6. (c) The number of heterozygotes is 48. (d) The number of homozygous recessive individuals is 16. (e) The number of homozygous dominant individuals is 36.

Question 40

One spring, a dust storm blankets the usually green garden of the Fraggles in gray. The green Fraggles therefore become visible to the Gorgs, who tend the gardens and try to kill the Fraggles to protect their crops. The gray Fraggles, however, blend easily into the dusty background. How might this event affect microevolution in the Fraggles? What mode of natural selection does this represent?

Answer 40

The homozygous recessive condition (gray) has a better chance of survival and will therefore have greater reproductive success. Their numbers will increase in future generations. This represents directional selection.

Question 41

Describe examples of directional, disruptive, and stabilizing selection other than those mentioned in the chapter.

Answer 41

Many examples possible. Below are a few:
Directional: increasing pesticide resistance, increasing body size in horse evolution
Disruptive: banding or no banding patterns in Lake Erie water snakes, different body shapes in cichlid fish from the same cohort in African lakes
Stabilizing: clutch size in birds, anatomical structures in alligators and horseshoe crabs

Question 42

How does sexual selection maintain sexual dimorphism?

Answer 42

If a trait seems harmful but somehow increases an individual’s reproductive success, it will become more common in the population.

Question 43

One of the most striking examples of convergent evolution occurs among animals that permanently live in caves. Among other shared traits, many of these species are eyeless. Develop a hypothesis to explain how an eyeless species could evolve from an ancestral population with eyes. How does your hypothesis compare to how Lamarck might have explained it?

Answer 43

The allele for eyelessness is recessive but is carried in the population by a few heterozygous individuals. In every generation there would be a chance that some offspring receive the recessive allele from both parents (homozygous recessive). In normal environments, these offspring would be at a selective disadvantage and most would not breed. In a cave, they would not be at a disadvantage and could live to mate. If two homozygous recessive individuals mate, then all of their offspring are homozygous recessive (eyeless). The allele frequency of the population slowly shifts toward recessive; a larger percentage of each successive generation would be eyeless. Lamarck might have suggested that in the cavefish did not use their eyes and so they lost them. This loss was passed on to their offspring.

Question 44

What is the biological definition of evolution

Answer 44

The biological definition of evolution is the change of allele frequencies in a population over time.

Question 45

Add the terms genotype, phenotype, allele frequencies, founder effect, bottleneck effect, and sexual selection to this concept map.

Answer 45

“Evolution” leads with “alters” to “Allele frequency”. “Nonrandom mating” leads with “is not seen in nature due to” to “Sexual selection”. “Founder effect” and “Bottleneck effect” lead with “are specific types of” to “Genetic drift”. “Mutation” leads with “alters an organism’s” to “Genotype”, which leads with “partly determines” to “Phenotype”.

Question 46

Natural selection

Answer 46

Natural selection changes allele frequency by selecting against alleles that reduce the chance of survival and selecting for alleles that enhance the chance of survival.

Question 47

Describe the three modes of natural selection.

Answer 47

Phenotypes with a range of expressions in a population, from common to extremes, are subject to selective pressures. Directional selection chooses for one extreme or against one extreme of a phenotype. Disruptive selection chooses against the average phenotype, leaving different extremes of a phenotype in the population. Stabilizing selection chooses against the extreme phenotypes in the population, leaving the average phenotype.

Question 47

Georges Cuvier,

Answer 47

Georges Cuvier suggested that catastrophic events may cause extinctions and that nature can act abruptly.

Question 48

Georges-Louis Buffon,

Answer 48

Georges Buffon said that species change as they spread from their original location.

Question 49

Jean Baptiste de Lamarck,

Answer 49

Jean Baptiste de Lamarck proposed the inheritance of acquired characteristics.

Question 50

Charles Lyell,

Answer 50

Charles Lyell renewed the argument of uniformitarianism and applied gradual geologic change to the history of the Earth and life; Lyell also suggested that the Earth was much older than 6000 years, allowing plenty of time for evolution by means of natural selection to occur.

Question 51

Thomas Malthus

Answer 51

Thomas Malthus illustrated that populations produce many offspring and compete for resources. Darwin extended Malthus’ theory, suggesting that those individuals that are able to obtain resources best would be most likely to survive and reproduce.

Question 52

Mutation

Answer 52

Mutation changes allele frequency by introducing new alleles.

Question 53

Genetic drift

Answer 53

Genetic drift changes allele frequency by chance.

Question 54

Nonrandom mating

Answer 54

Nonrandom mating changes allele frequency by selecting for traits that other mates find attractive.

Question 55

Gene Flow

Answer 55

Gene flow changes allele frequency by moving alleles from one population to another.