Exam 1 Flashcards
Micro-evolutions occur when ________
changes in allele frequencies in a population occur over generations
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.
Which of the following descriptions illustrates phenotype variation caused by environment?
diet of caterpillars changes their morphology
Genetic variation ________.
must be present in a population before natural selection can act upon the population
Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, ________.
the allele’s frequency should not change from one generation to the next
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?
0.09
Which Hardy-Weinberg condition is affected by population size?
genetic drift
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
If individuals tend to mate within a subset of the population, there is ________.
nonrandom mating
Which one of the following conditions would allow gene frequencies to change by chance?
small populations
Which of the following is the most predictable outcome of increased gene flow between two populations?
decreased genetic difference between the two populations
Natural selection changes allele frequencies because some ________ survive and reproduce better than others
individuals
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?
stabilizing selection
Macroevolution is ________.
evolution above the species level
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?
a behavioral reproductive isolating mechanism
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?
No; they still can interbreed.
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
explain why genetic variation within a population is a
prerequisite for evolution.
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.
Of all the mutations that occur in a population, why do only a small fraction become widespread?
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.
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?
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.
In what sense is natural selection more “predictable”
than genetic drift?
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.
Distinguish genetic drift from gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population.
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
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.
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.
What is the relative fitness of a sterile mule? explain.
Zero, because fitness includes reproductive contribution to next generation, and a sterile mule cannot produce offspring.
explain why natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution in a population.
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
- Natural selection changes allele frequencies because some _________ survive and reproduce better than others
Individuals
No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is
the reshuffling of alleles in sexual reproduction.
If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?
gene variability = 0%; number of alleles = 1
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
Genetic Drift
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?
0.42
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.
(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.
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.
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.
Summarize key differences between allopatric and sympat- ric speciation. Which type of speciation is more common, and why?
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.
Describe two mechanisms that can decrease gene flow in sympatric populations, thereby making sympatric speciation more likely to occur.
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
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
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.
The largest unit within which gene flow can readily occur is a
Species
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?
Temporal Isolation
According to the punctuated equilibria model
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
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?
The two forms interbreed often in nature, and their
offspring survive and reproduce well
Which of the following factors would not contribute to allopatric speciation?
Gene flow between the two populations is extensive.
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
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’.
explain the consequences of plate tectonics for life
on earth.
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.
What factors promote adaptive radiations?
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.
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.
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.
Fossilized stromatolites
resemble structures formed by bacterial com- munities that are found today in some shallow marine bays.
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?
the evolution of cellular respiration, which used oxygen to
help harvest energy from organic molecules
Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?
The species became separated by convergent evolution.
Adaptive radiations can be a direct consequence of three of the following four factors. Select the exception.
vacant ecological niches
