Exam 1

Question 1

Micro-evolutions occur when ________

Answer 1

changes in allele frequencies in a population occur over generations

Question 2

Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?

Answer 2

Each bird’s survival was strongly influenced by the depth and strength of its beak as the drought persisted.

Question 3

Which of the following descriptions illustrates phenotype variation caused by environment?

Answer 3

diet of caterpillars changes their morphology

Question 4

Genetic variation ________.

Answer 4

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

Question 5

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, ________.

Answer 5

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

Question 6

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?

Answer 6

0.09

Question 7

Which Hardy-Weinberg condition is affected by population size?

Answer 7

genetic drift

Question 8

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?

Answer 8

a genetic bottleneck

Question 9

If individuals tend to mate within a subset of the population, there is ________.

Answer 9

nonrandom mating

Question 10

Which one of the following conditions would allow gene frequencies to change by chance?

Answer 10

small populations

Question 11

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

Answer 11

decreased genetic difference between the two populations

Question 12

Natural selection changes allele frequencies because some ________ survive and reproduce better than others

Answer 12

individuals

Question 13

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?

Answer 13

stabilizing selection

Question 14

Macroevolution is ________.

Answer 14

evolution above the species level

Question 15

Three populations of crickets look very similar, but the males have courtship songs that sound different. What function would this difference in song likely serve if the populations came in contact?

Answer 15

a behavioral reproductive isolating mechanism

Question 16

The peppered moth provides a well-known example of natural selection. The light-colored form of the moth was predominant in England before the Industrial Revolution. In the mid-19th century, a dark-colored form appeared. The difference is produced by a dominant allele of one gene. By about 1900, approximately 90% of the moths around industrial areas were dark colored, whereas light-colored moths were still abundant elsewhere. Apparently, birds could readily find the light moths against the soot-darkened background in industrial areas and, therefore, were eating more light moths. Recently, use of cleaner fuels has greatly reduced soot in the landscape, and the dark-colored moths have been disappearing. Under the Biological Species Concept, should the two forms of moths be considered separate species?

Answer 16

No; they still can interbreed.

Question 17

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 ________

Answer 17

natural selection is generally limited to modifying structures that were present in previous generations and in previous species

Question 18

explain why genetic variation within a population is a
prerequisite for evolution.

Answer 18

Within a population, genetic differences among individuals provide the raw material on which natural selection and other mechanisms can act. Without such differences, allele frequencies could not change over time - and hence the population could not evolve.

Question 19

Of all the mutations that occur in a population, why do only a small fraction become widespread?

Answer 19

Many mutations in somatic cells that do notpro d gametes and so are lost when the organism dies. Of mutations that do occur in cell lines that produce gametes, many do not have a phenotypic affect on which natural selection can act others have a harmful affect, and are thus unlikely to increase in frequency because they decrease the reproductive success of their bearers.

Question 20

A population has 700 individuals, 85 of genotype AA, 320 of genotype Aa, and 295 of genotype aa. What are the frequencies of alleles A and a?

Answer 20

Each individual has two alleles, so the total number of alleles is 1,400. To calcu- late the frequency of allele A, note that each of the 85 individuals of genotype AA has two A alleles, each of the 320 individuals of genotype Aa has one A allele, and each of the 295 individuals of genotype aa has zero A alleles. Thus, the frequency (p) of allele A is p =((2 x85) + (1x 320) + (0 * 295))/1,400 = 0.35
There are only two alleles (A and a) in our population, so the frequency of allele a must be q = 1 - p = 0.65.

Question 21

In what sense is natural selection more “predictable”
than genetic drift?

Answer 21

Natural selection “predictable” in that it alters allele frequencies in a nonrandom way: tends to increase frequency of alleles that increase organism’s reproductive success in its environment and decrease frequency of alleles that decrease organism’s reproductive success.

Question 22

Distinguish genetic drift from gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population.

Answer 22

Genetic drift results from chance events that cause allele frequencies to fluctuate at random from generation to generation; within population, this process tends to decrease genetic variation over time. Gene flow is transfer of alleles between populations, a process that can introduce new alleles to a population and may increase its genetic variation

Question 23

A locus that affects susceptibility to a degener- ative brain disease has two alleles, V and v. In a population, 16 people have genotype VV, 92 have genotype Vv, and 12 have genotype v v. Is this population evolving? explain.

Answer 23

There are 120 individuals in the population, so there are 240 alleles. Of these, there are 124 V alleles—32 from the 16 VV individuals and 92 from the 92 Vv individuals. Thus, the frequency of the V allele is p = 124/240 = 0.52; hence, the frequency of the v allele is q = 0.48. Based on the Hardy-Weinberg equation, if the population were not evolving, the frequency of genotype VV should be p2 = 0.52 × 0.52 = 0.27; the frequency of genotype Vv should be 2pq = 2 × 0.52 × 0.48 = 0.5; and the frequency of genotype vv should be q2 = 0.48 × 0.48 = 0.23. In a population of 120 individuals, these expected genotype frequencies lead us to predict that there would be 32 VV individuals (0.27 × 120), 60 Vv individuals (0.5 × 120), and 28 vv individuals (0.23 × 120). The actual numbers for the population (16 VV, 92 Vv, 12 vv) deviate from these expectations. This indicates that the population is not in Hardy-Weinberg equilibrium and hence may be evolving at this locus.

Question 24

What is the relative fitness of a sterile mule? explain.

Answer 24

Zero, because fitness includes reproductive contribution to next generation, and a sterile mule cannot produce offspring.

Question 25

explain why natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution in a population.

Answer 25

Only natural selection consistently results in increase in frequency of alleles that enhance survival or reproduction. Thus, natural selection is only mechanism that consistently leads to adaptive evolution

Question 26

1. Natural selection changes allele frequencies because some _________ survive and reproduce better than others

Answer 26

Individuals

Question 27

No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is

Answer 27

the reshuffling of alleles in sexual reproduction.

Question 28

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?

Answer 28

gene variability = 0%; number of alleles = 1

Question 29

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. 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 most likely resulted from

Answer 29

Genetic Drift

Question 30

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

Answer 30

0.42

Question 31

a) Which species concept(s) could you apply to both asexual and sexual species? (b) Which would be most useful for identifying species in the field? explain.

Answer 31

(a) All except the biological species concept can be applied to both asexual and sexual species because they define species on the basis of characteristics other than the ability to reproduce. In contrast, the biological species concept can be applied only to sexual species. (b) The easiest species concept to apply in the field would be the morphological species concept because it is based only on the appearance of the organism. Additional information about its ecological habits, evolutionary history, and reproduction is not required.

Question 32

Suppose two bird species live in a forest and are not known to interbreed. one species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and produce viable, fertile offspring. What type of reproductive barrier most likely keeps these species separate in nature? explain.

Answer 32

Because these birds live in fairly similar environments and can breed successfully in captivity, the reproductive barrier in nature is probably prezygotic; given the species' differences in habitat preference, this barrier could result from habitat isolation.

Question 33

Summarize key differences between allopatric and sympat- ric speciation. Which type of speciation is more common, and why?

Answer 33

In allopatric speciation , a new species forms while in geographic isolation from its parent; In sympatric speciation a new species forms in absence of geographic isolation, geographic isolation greatly reduces the gene flow of populations, allopatric is more common.

Question 34

Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur.

Answer 34

Gene flow for species that live in a area can be reduced in many ways. In some species such as plant , gene flow is locked by a change in chromosome numbers. Gene flow can also be reduced in sympatric populations by habitat differation and sexual selection

Question 35

is allopatric speciation more likely to occur on an island close to a mainland or on a more isolated island of the same size? explain your prediction

Answer 35

less likely to occur on island near mainland than on isolated island of same size. We expect this result because continued gene flow between mainland populations and those on a nearby island reduces chance that enough genetic divergence will take place for allopatric speciation to occur.

Question 36

The largest unit within which gene flow can readily occur is a

Answer 36

Species

Question 37

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent?

Answer 37

Temporal Isolation

Question 38

According to the punctuated equilibria model

Answer 38

most new species accumulate their unique features rela- tively rapidly as they come into existence, then change little for the rest of their duration as a species

Question 39

Bird guides once listed the myrtle warbler and Audubon’s warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?

Answer 39

The two forms interbreed often in nature, and their offspring survive and reproduce well

Question 40

Which of the following factors would not contribute to allopatric speciation?

Answer 40

Gene flow between the two populations is extensive.

Question 41

Plant species A has a diploid chromosome number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be

Answer 41

For, plant A 2n=12; For plant B 2n=16 so, 2n value for an allopolyploid plant is: 12+16 =28 So, the correct answer is '28'.

Question 42

explain the consequences of plate tectonics for life on earth.

Answer 42

Plate tectonics greatly affected the life on earth since the movement of the continental plates resulted to the change in the Earth's geography and climate which isolated different organisms from each other. These factors are driving forces for evolution, greatly affecting both the rates of speciation and extinction of different life forms on Earth.

Question 43

What factors promote adaptive radiations?

Answer 43

Adaptive radiation often happens after mass extinctions because it allows animals to occupy different niches and ecological roles and evolve because of it. Also, the migration to a new habitat in which few or different predators exist promotes adaptive radiation. Species that adapt can promote adaptive radiation in others by becoming food sources.

Question 44

Suppose that an invertebrate species was lost in a mass extinction caused by a sudden catastrophic event. Would the last appearance of this species in the fossil record necessarily be close to when the extinction actually occurred? Would the answer to this question differ depending on whether the species was common (abundant and widespread) or rare? explain.

Answer 44

In theory, fossils of both common and rare species would be present right up to the time of the catastrophic event, then disappear. Reality is more complicated because the fossil record is not perfect. So the most recent fossil for a species might be a million years before the mass extinction even though the species did not become extinct until the mass extinction. This complication is especially likely for rare species because few of their fossils will form and be discovered. Hence, for many rare species, the fossil record would not document that the species was alive immediately before the extinction.

Question 45

Fossilized stromatolites

Answer 45

resemble structures formed by bacterial com- munities that are found today in some shallow marine bays.

Question 46

he oxygen revolution changed Earth’s environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?

Answer 46

the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules

Question 47

Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?

Answer 47

The species became separated by convergent evolution.

Question 48

Adaptive radiations can be a direct consequence of three of the following four factors. Select the exception.

Answer 48

vacant ecological niches