bio exam 5
Three populations of crickets look very similar, but the males have different courtship songs. If the cricket populations were to contact each other in the wild, the different courtship songs would most likely function as which type of reproductive isolating mechanism?
behavioral
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?
behavioral isolation
Which of the following possible isolating mechanisms prevents individuals from wasting time and energy hybridizing with an individual of another species?
behavioral isolation
In evolutionary terms, an organism's relative 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.)
In a very large population, a measurable trait has the distribution pattern shown in the diagram. Assume the trait is genetically determined. If there is no gene flow and the curve shifts to the left or to the right, which of the following processes is most likely occurring?
directional selection
Which of the following processes best describes the cause of a bottleneck effect?
drastic decrease in the size of the population
Cystic fibrosis is a genetic disorder in humans where the person has two homozygous recessive alleles for the gene. If the disease is left untreated, it causes severe health problems in the individual. 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?
f(A1) = 0.9700, f(A2) = 0.0300
The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in allele frequencies at many loci from all other populations, including those in their original homeland. Which of the following mechanisms most likely explains the genetic uniqueness of this population?
founder effect and genetic drift
Two juniper trees (Juniperus scopulorum and J. monosperma) have overlapping geographic ranges. Pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species. Which of the following isolating mechanisms keeps the two species separate?
gametic isolation
Which of the following are causes of evolutionary change?
gene flow genetic drift natural selection mutation
A windstorm transports a few seeds of a plant species from Island A, where the species is abundant, to Island B, where prior to this event the plant species was not found. The environmental conditions on the two islands are very similar, but the islands are located far away from one another. Over time, a small population of this plant becomes established on Island B. A biologist samples plants on both islands and finds that allele frequencies on Island A differ substantially from allele frequencies on Island B at several genetic loci not known to affect survival or reproduction. Based on this information, the observed genetic changes mostly likely resulted from
genetic drift
The effect of which Hardy-Weinberg condition is affected by population size?
genetic drift
Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?
genetic drift (Genetic drift is due to chance events that alter allele frequencies.)
Which of the following is the first step in allopatric speciation?
geographic isolation (Allopatric speciation occurs when a population of organisms is geographically separated long enough for significant changes to occur. After a period of time, the populations may no longer be able to interbreed.)
Two populations of birds with somewhat different coloration live on opposite sides of a peninsula. The habitat between the populations is not suitable for these birds. When birds from the two populations are brought together in captivity, they interbreed and produce fertile young whose appearance is intermediate between the two parents. In the wild, the two populations remain separate as a result of which of the following factors?
habitat isolation
Natural selection changes allele frequencies because some _______ survive and reproduce better than others.
individuals
If you had trouble with this question, review the following material: Since, the environmental conditions on the two islands are very similar and the genetic loci sampled are not known to affect survival or reproduction, it is not likely that the observed differences were caused by natural selection. Gene flow causes populations to become more similar genetically over time, not more different. However, the observed differences could well be caused by genetic drift, the fluctuation of allele frequencies from one generation to the next in a population due to chance events; for example, the founder effect often causes members of a new population (such as that on Island B) to differ genetically from members of the source population (Island A).
information
Which of the following is true of microevolution?
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)
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.)
What is the only evolutionary mechanism that consistently leads to adaptive evolution?
natural selection (Because natural selection has a sorting effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.)
If individuals tend to mate within a subset of the population, there is ________.
no random mating
Which of these is an example of temporal isolation between two species?
one species is nocturnal, and the other species is not ( In temporal isolation, two species that breed during different times of the day cannot mix their gametes.)
According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if __________ is the only process acting on the gene pool.
random mating (Random sexual reproduction does not change the frequency of alleles in the gene pool.)
Part complete Many songbirds breed in North America in the spring and summer, and then migrate to Central and South America in the fall. They spend the winter in these warmer areas where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, species X and species Y, overwinter together in mixed flocks in Costa Rica. In spring, species X goes to the east coast of North America, and species Y goes to the west coast. Which of the following factors most likely keeps these species separate?
the two species reproduce in different geographic areas
The value of the Hardy-Weinberg equation is that it allows scientists to perform which of the following assessments?
to detect whether an evolutionary force is acting on a population
Which of the following provides an example of a mechanical isolation as a prezygotic barrier?
two snails have shells that spiral in different directions
The evolutionary effects of genetic drift are greatest when __________.
the population size is small (Changes in the gene pool of a small population are frequently due to genetic drift.)
Consider a population of wildflowers in which the frequency of the red allele CR is p = 0.7. What is the frequency of the white allele (CW ) in this population?
0.3 (If the frequency of the red allele is p, and the frequency of the white allele is q, we know that p + q = 1. Since p = 0.7, we know that q = 0.3.)
In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.2. What is the frequency of individuals that are heterozygous for this allele?
0.32
What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
0.4 (The calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20 + 80 + 100) total individuals = 0.4, the frequency of the A1A2 genotype.)
In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.1. What is the frequency of individuals with A1A1 genotype?
0.81
Which of the following statements is accurate with regard to a population in Hardy-Weinberg equilibrium?
Allele frequencies should not change from one generation to the next.
Which of the following are basic components of the Hardy-Weinberg model?
Frequencies of two alleles in a gene pool before and after many random matings (Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next.)
What are the expected genotype frequencies in the offspring generation?
Under Hardy-Weinberg equilibrium, the frequency of genotype CRCR (red flowers) in the offspring generation is expected to be p 2, or 0.49. The frequency of genotype CRCW (pink flowers) in the offspring generation is expected to be 2pq, or 0.42. The frequency of genotype CWCW (white flowers) in the offspring generation is expected to be q 2, or 0.09.
An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population has broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, which of the following processes most likely caused the change?
a bottleneck effect
Which of the following evolutionary forces could create new genetic information in a population?
Mutation (Mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.)
Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?
Selection (Selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.)
Lions and tigers sometimes breed in zoos, but hybrids have not been seen in nature and even in zoos they do not reproduce well. Which of the following statements is the best conclusion that can be derived from this information?
The biological species concept can be applied because species are, in part, defined by the inability to produce viable, fertile offspring with other species.
In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of the allele A2 is 0.3. What is the frequency of individuals that are homozygous for this allele?
0.09
How do these molecular and cellular events lead to emergent properties at the individual and population levels of biological organization? Match the terms in the left column to the appropriate blanks in the sentences on the right. Terms can be used once, more than once, or not at all.
HETEROZYGOTES for the sickle-cell allele are protected against the most severe effects of malaria because the organism destroys sickled ERYTHROCYTES rapidly, killing the parasites in them. Selection thereby favors against homozygous DOMINANT individuals, who are more vulnerable to the effects of the sickness, and also against homozygous RECESSIVE individuals, who develop sickle-cell disease. As a result, the frequency of the sickle-cell allele reaches relatively HIGH levels in areas where malaria is widespread. HETEROZYGOTES have greater fitness than do HOMOZYGOTES, thereby exhibiting a heterozygote advantage.
Consider a wildflower population with the following allele and genotype frequencies. Frequency of the CR allele: p = 0.6 Frequency of the CW allele: q = 0.4 Frequency of CRCR : 50% Frequency of CRCW : 20% Frequency of CWCW : 30% Is this population in Hardy-Weinberg equilibrium?
No, the frequency of genotype CRCW is too low. (To tell if this population is in Hardy-Weinberg equilibrium, you should calculate the expected genotype frequencies based on the allele frequencies. The frequency of genotype CRCR (red flowers) in the offspring generation is expected to be p 2 = (0.6)2 = 0.36. The frequency of genotype CRCW (pink flowers) is expected to be 2pq = 2(0.6)(0.4) = 0.48. The frequency of genotype CWCW (white flowers) in the offspring generation is expected to be q 2 = (0.4)2 = 0.16. Comparing these expected values with the actual genotype frequencies in the population, you can see that the frequency of genotype CRCW is too low while the frequencies of the other two genotypes are too high.)
What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene?
The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2 , and A2A2 , respectively. (The expected frequency of the A1A1 genotype is p 2 = (0.8)(0.8) = 0.64; the expected frequency of the A1A2 genotype is 2pq = 2(0.8)(0.2) = 0.32; the expected frequency of the A2A2 genotype is q 2 = (0.2)(0.2) = 0.04. To verify your calculations, confirm that the three frequencies add up to one.)
Some geographic areas contain two closely related species of birds (sympatry), while other areas contain only one of the species (allopatry). Males from allopatric populations look very similar to each other, but males in the sympatric populations look different from each other and from both allopatric types of males. Which of the following outcomes is most likely if a female in a sympatric area is courted by a male that migrated into the area from an allopatric area?
The female is less likely to mate with the immigrant than with a male native to the area
What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
The frequency of the A1 allele is 0.3. (The frequency of the A1 allele is p = (number of A1 alleles) / (total of all alleles) = [(2 ( 20) + 80] / [(2 × 20) + (2 × 80) + (2 × 100)] = 0.3.)
Which of the following statements is not a part of the Hardy-Weinberg principle?
The genotype frequencies in the offspring generation must add up to two. (This statement is not true; the genotype frequencies in the offspring generation must add up to one.)
Almost all peppered moths in England were light colored before the Industrial Revolution. However, some dark forms were collected-the dark color is determined by a single, dominant allele of one gene. The bark of trees became darker during the Industrial Revolution in areas where heavy coal use in factories caused pollution. By about 1900, approximately 90% of the moths around industrial areas were dark, whereas light-colored moths were still abundant elsewhere. Apparently, birds could readily find the light moths against the dark trees in industrial areas and, therefore, were eating more light moths. Recently, use of cleaner fuels has resulted in tree bark becoming lighter again and the dark-colored moths have been disappearing. Which of the following statements best explains whether we should consider the forms different species?
They are NOT different species-as shown by the fact that they can interbreed.
The common edible frog of Europe is a hybrid between two named species, Rana lessonae and Rana ridibunda. The hybrids were first described in 1758 and have a wide distribution, from France across central Europe to Russia. Both male and female hybrids exist, but when they mate among themselves, they rarely produce offspring. Which of the following statements is the best inference about the two Rana species?
They are different species and postzygotic isolation exists between the two frog species.
True or false? The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.
True (These are the five assumptions of the Hardy-Weinberg model.
Which one of the following conditions would most likely cause allele frequencies to change by chance?
small populations
Which of the following organisms would be LEAST able to cross a geographic barrier of water that could lead to allopatric speciation?
small rodents
Sympatric speciation is __________.
the appearance of a new species in the same area as the parent population (It is due to a radical change in the genome)
