Chapter 23 :|
A gene is present in the form of three alleles in a population, P, p1, and p2. If the frequency of the P allele is 0.6, and the frequency of the p1 allele is 0.2, then what is the frequency of the p2 allele?
0.2
In a population of frogs, a gene is found in two forms - D, and d. The numbers of individuals with different genotypes for that gene are 30 (DD), 18 (Dd), and 12 (dd). What is the frequency of the heterozygous genotype?
0.30
Which of the following best describes the relationship between a genotype's fitness and its frequency in negative frequency-dependent selection?
As the frequency of a genotype increases, its fitness decreases.
Inbreeding and outbreeding can cause certain features of populations to deviate from Hardy-Weinberg equilibrium. From the list below, choose the statements that describe commonalities between inbreeding and outbreeding. Assume that no other evolutionary processes are acting on the genes in question.
Neither inbreeding nor outbreeding affect the allele frequencies in a population. Both inbreeding and outbreeding alter the relative proportions of genotypes in a population.
Consider a population of a hypothetical animal, whose fur color is determined by a single gene, called Col. From the list below choose all conditions that must be met in order for this population to be in Hardy-Weinberg equilibrium for the Col gene.
No new mutations in the Col gene No natural selection Animals in the population mate randomly, regardless of their genotype for the Colgene
Which of the following (choose all that apply) are conditions that must be met in order for a population to be in Hardy-Weinberg equilibrium for a specific gene of interest?
No new mutations should be appearing in the gene of interest. All of the different genotypes (with respect to the gene of interest) must have equal reproductive success (no selection). The population must be large enough so that no genetic drift is occurring.
You are observing two populations of the same animal species. Population 1 consists of 46 individuals, while population 2 consists of 3325 individuals. Which population is more susceptible to genetic drift?
Population 1 is more susceptible.
Which of the following describes a situation, in which the predominant genotype in a population in Hardy-Weinberg equilibrium is the heterozygote? Assume that the gene of interest has only two alleles: G, and g.
The allele frequencies of both G and g are intermediate in value.
A founding population usually has lower genetic diversity than the original population it came from. For those alleles that are shared by the two populations, how are allele frequencies different (or similar)?
Usually, the allele frequencies in the founding population are very different from those of the original population.
In _____ selection, natural selection favors the maintenance of two or more alleles in a population. An example of that is the phenomenon of heterozygote advantage.
balancing
In a specific population, a gene is present as two alleles: D, and d. For every 100 ddindividuals that survive to reproduce, 18 DD and 99 Dd individuals survive to reproduce as well. Which of these three genotypes has the highest Darwinian fitness and what is its value (w)? Assume that all individuals that survive to reproduce have roughly the same number of offspring.
dd, wdd = 1.0
Most mutations are ______.
deleterious or neutral
In _____ selection, individuals at one extreme of a phenotypic distribution are more likely to survive and reproduce in a particular environment.
directional
The term genetic _____ refers to any random change in the frequencies of alleles in a population.
drift
The ______ of a population is the sum of the frequencies of all genotypes, each one multiplied by its respective relative fitness.
mean fitness
Most of the traits in a healthy natural population exhibit some level of variation, or _____, that is, they are found in two or more forms.
polymorphism
In genetics, a _____ of a sexually reproducing species consists of a group of individuals of that species, which occupy the same region, and can successfully interbreed with each other.
population
You are studying migration of individuals from a donor population to a recipient population. The frequency of the allele R is 0.6 in the donor population, and 0.8 in the recipient population. The recipient population contained 120 individuals, and 40 individuals migrated into it from the donor population. What will the change in frequency of R be in the conglomerate population after the migration event?
-0.05
A gene is found in two forms in a population of plants. The two alleles are denoted as B, and b. You determine that the frequency of the B allele in this population is 0.2. If this population was in a Hardy-Weinberg equilibrium, calculate the probability of a heterozygote in the next generation.
0.32
In a population of lizards, a gene is found in two forms, B, and b. The number of animals with the three possible genotypes for this gene is as follows: BB - 24; Bb - 42; bb - 9. What is the frequency of the B allele in this population?
0.6
Consider a population and a gene present in this population as two alleles: F, and f. For every 10 Ff individuals that survive to reproduce, 8 FF and 4 ff individuals survive to reproduce as well. If we assume that all individuals that survive to reproduce have roughly the same number of offspring, what is the relative fitness of the FF genotype in this case?
0.8
You are studying a population and a gene within that population with two alleles, M and m. After determining the genotypes of all the individuals in the population you calculate the observed and expected numbers of individuals for the three genotypes as follows. Observed individuals: MM - 200; Mm 123; mm - 14. Expected individuals: MM - 202; Mm - 117; mm - 17. What is the chi square value calculated based on these observations?
0.86
The sum of the frequencies of all of the alleles of a particular gene in a population is always _____.
1
You are studying a population and a gene within that population with two alleles, D and d. After determining the genotypes of all the individuals in the population you calculate the observed and expected numbers of individuals for the three genotypes as follows. Observed individuals: DD - 332; Dd 90; dd - 6. Expected individuals: DD - 340; Dd - 84; dd - 4. What is the Chi-square value calculated based on these observations?
1.62
Repetitive sequences are composed of a certain sequence that is repeated many times throughout the genome of a species. What is the typical size of the sequence that is being repeated?
A few to a few thousand base pairs
Which of the following correctly defines a population of sexually reproducing species for the purposes of population genetics?
A group of individuals that occupy the same area and can interbreed with each other
Which of the following is a situation in which directional selection may be observed?
A new allele, which promotes higher fitness in organisms that carry it, is introduced in a population (for example, by a random mutation).
Consider a very rare autosomal recessive disease, which affects only 1 in 40,000 individuals in a population. What is the expected frequency of heterozygotes in this population?
About 1%
Consider a population of cheetahs, inhabiting a protected area in Africa. In 2012, there were 112 cheetahs in this population. During that year, 60 of those animals reproduced and 48 new cubs were born. What constitutes the gene pool of the new generation made of those 48 new cubs?
All of the alleles of every gene that were passed from the 60 parents to the 48 new cubs
You are studying a rare disease, which affects 1 out of 10000 individuals. The disease is caused by a gene with two alleles: D, and d. Individuals with a dd genotype are affected, while individuals with a Dd phenotype are unaffected carriers. What is the expected frequency of unaffected carriers in the population, assuming this gene is in Hardy-Weinberg equilibrium?
Approximately 2%
You are studying two populations of the same species. Population A consists of 100 individuals, while population B consists of 1,000 individuals. Population ______ will have a higher number of new mutations appearing in the next generation, and population ______ will have a higher likelihood of fixation of new mutations.
B; A
Which of the following is NOT a reason for differences in the reproductive success of different genotypes in a population?
Certain genotypes are more likely to continue to live after surviving to reproductive age.
The relative (compared to other genotypes) likelihood that a genotype will contribute its alleles to the next generation is known as
Darwinian fitness
New mutations can be deleterious, neutral, or beneficial. Which of those three general types of mutations are most likely to occur?
Deleterious and neutral mutations are much more likely than beneficial mutations.
You are studying a population of birds that has recently become established on an island some 1,000 km from the mainland. On the mainland, these birds mostly consume fleshy fruits, however, on the island they are forced to eat nuts that have to be cracked open with a strong beak. What type of selection is most likely to occur for genes that determine the size and strength of the beak in these birds?
Directional selection
Which type of selection is also known as diversifying selection because it tends to favor the survival of two or more different phenotypes in a heterogeneous environment?
Disruptive selection
You are studying two areas inhabited by a species of frog. In area X, ponds inhabited by the frogs are far apart and frogs rarely move from one pond to another. In area Z, ponds inhabited by these frogs are connected by a man-made system of channels, which allows free movement of frogs between ponds. Which of the following accurately describes differences in allele frequencies between different ponds within each area?
Each pond in area X should have different allele frequencies, while the allele frequencies in all ponds in area Z are likely to be very similar.
Over time, genetic drift can lead to the fixation of an allele. What types of alleles are usually fixed by drift?
Genetic drift is random, so deleterious, beneficial, or neutral alleles can become fixed.
Which of the following phenomena is responsible for introducing new genetic variation in a population?
Mutation
You are studying two populations of an animal species. Population A is made of 300 individuals, while population B is made of 56,000 individuals. You are interested in following a new mutation until it gets fixed by genetic drift. In which of the two populations will it take fewer generations for a new allele to be fixed?
Population A
What is the most common type of polymorphism found in natural populations, including human populations?
SNPs
Which of the following are likely reasons for differences in the reproductive success of different genotypes in a population?
Some genotypes are more likely to find mates than others. Some genotypes are more fertile than others. Some genotypes are more likely to survive to reproductive age than others.
Which type of selection tends to select against extreme phenotypes for a quantitative trait, because individuals with intermediate phenotypes have the highest relative fitness values?
Stabilizing selection
A scientist is studying two populations of the same species of birds - one in Michigan, and one in Montana. Both populations are relatively large (with more than 10,000 individuals each). However, the Michigan population has a much lower genetic diversity than the Montana population. Which of the two populations is most likely to have experienced a bottleneck and which of the two populations is currently more susceptible to genetic drift?
The Michigan population likely experienced a bottleneck in the past. Both populations are equally susceptible to genetic drift.
What does the selection coefficient measure?
The extent to which a genotype is selected against
Choose the two most important results of the founder effect on the newly founded population.
The founding population typically has less genetic diversity than the original population. The founding population typically has very different allele frequencies from those of the original population.
The HbS allele for the human β-globin gene is found in relative high frequencies in certain human populations living in areas where malaria is endemic, despite the fact that individuals homozygous for this allele exhibit sickle cell anemia. What explains this observation?
The heterozygous genotype (HbAHbS) is more resistant to malaria than either of the homozygous genotypes.
What is the effect of population size (N) (if any) on the probability of fixation of a new allele due to genetic drift?
The higher N is, the lower the chance that a new mutation will become fixed.
Is the size of a population related to the average number of generations needed to achieve fixation of a newly appeared mutation, and how?
The larger the population, the more generations will be required, on average, to achieve fixation of a new allele.
A population is undergoing directional selection for a gene with two alleles: G, and g. The most fit genotype is GG (relative fitness 1), while the Gg and gg genotypes both have relative fitnesses of 0.5. Which of the following is expected to happen after several generations (assuming that the environment, in which this population lives, is not changing)?
The mean fitness of the population will increase.
How is the allele frequency of a population calculated?
The number of copies of the allele in the population is divided by the total number of all the alleles for the same gene in the population.
Consider a population and a gene that has two alleles in this population, designated as P and p. If you divide the number of all the copies of the p allele in the population by the total number of copies of both alleles (P and p) in the population, you will calculate the ______ frequency of the ______.
allele; p allele
In a natural setting, migration between two populations usually occurs in a bidirectional manner in which some individuals of each population migrate to the other population. As a result of such bidirectional movement, differences in allele frequencies ______.
are reduced
For random mating to occur, individuals must choose their mates irrespective of their genotype/phenotype. When this condition is violated, non-random mating is occurring, also known as _____ mating.
assortative
A healthy population can become highly susceptible to genetic drift if its size is dramatically reduced due to natural phenomena, such as earthquakes or droughts. This is known as the ______ effect.
bottleneck
A population that has experienced a bottleneck is highly susceptible to genetic drift ______.
during the initial bottleneck and during the generations following the bottleneck when the population size is small
A group of individuals from a larger population can migrate to a new area and establish a colony, which will be highly susceptible to genetic drift. This is known as the ______ effect.
founder
Sometimes populations become susceptible to genetic drift via the _____ effect. This happens when a small group of individuals separates from a larger population and migrates to a different site, where it establishes a colony.
founder
In order to derive the Hardy-Weinberg equation, the two scientists assumed that
gametes are independently chosen at random from the population's gene pool.
When individuals migrate, alleles can be transferred from one population to another population. This is commonly referred to as
gene flow
The ______ of a population consists of all of the alleles of every gene in all of the individuals of that population.
gene pool
Consider a population and a gene that has two alleles in this population, designated as D and d. If you divide the number of individuals with the genotype DD by the total number of individuals in the population, you will calculate the ______ frequency of the ______.
genotype; DD genotype
Consider a single gene with two alleles in a population of wild birds. A situation in which the heterozygotes for that gene have higher fitness than the two homozygote genotypes is known as _____ _____. In this situation, an equilibrium is reached, in which both alleles of the gene are maintained in the population.
heterozygote advantage
When the heterozygotes for a specific gene have higher fitness than either of the corresponding homozygote genotypes (assume a single gene with two alleles), we are observing a situation called
heterozygote advantage
The mechanism of evolution through _____ _____ states that those individuals better adapted to their environment are more likely to survive and reproduce.
natural selection
The mechanism of evolution through _____ _____ was proposed by Charles Darwin and Russel Wallace in the 1850s.
natural selection
In certain cases, the fitness of a genotype may be dependent on its frequency. When the fitness of a genotype decreases when its frequency increases, the pattern of natural selection is referred to as _____-_____ dependent selection.
negative frequency
Genetic drift is the ______ in a population.
random change of allele frequencies
Genotypes that have lower relative fitnesses are selected against. The extent of that selection is measured by s, the _____ _____
selection coefficient
Mutations occur when the DNA of an organism changes. Changes often happen in gene _____, but may also involve the structure and number of chromosomes.
sequences
_____ selection acts on quantitative traits determined by multiple genes. In this type of selection, individuals with intermediate phenotypes have higher fitness and are selected for, while extreme phenotypes are selected against.
stabilizing
In disruptive selection, ______.
two or more alleles are maintained in a heterogeneous environment
Consider a population for which you know the allele composition of three genes. Gene A has three alleles in the following proportions: A1 - 34.4%, A2 - 30%, A3 - 35.6%. Gene B has two alleles in the following proportions: B1 - 67.1%, B2 - 32.9%. Gene C has two alleles in the following proportions: C1 - 99.2%, C2 - 0.8%. Which of those genes is(are) polymorphic?
A and B only
Consider two populations of the same species and a gene that is found in two alleles in both populations (alleles D and d). Choose all values that need to be known in order to calculate the change in the frequency of the allele D if some individuals migrate from one of the populations into the other.
Frequency of D in the donor population Frequency of D in the original recipient population Proportion of the conglomerate population that is due to migrants from the donor population
If a population is in Hardy-Weinberg equilibrium for a gene with two alleles (G and g), and the frequency of the g allele is very low, we can predict that most of the organisms in this population will have the ______ genotype.
GG
Two types of factors can govern microevolution. On one hand, mutation is a constant source of new genetic variation. On the other hand, mechanisms that alter existing genetic variation, such as natural selection and genetic drift, can act to alter existing genetic variation. How do those two types of factors compare in terms of the magnitude of their effect on allele frequencies in a population?
Mutations have a negligible effect on allelic frequencies, while mechanisms such as natural selection and drift can have a dramatic effect.
How can we calculate the frequency of a specific genotype in a population?
The number of individuals with this genotype in the population is divided by the total number of individuals in the population.
Which of the following is the best definition of Darwinian fitness as it relates to population genetics?
The relative (compared to other genotypes) likelihood that a genotype will contribute alleles to the next generation
Which of the following best explains the high prevalence of the HbS allele of the human β-globin gene in populations living in areas of high malaria prevalence?
This gene is under balancing selection due to heterozygote advantage in those areas.
In certain populations, natural selection can favor the maintenance of two or more alleles in a population. An example of this is ______ selection.
balancing
Sometimes individuals at one extreme of a phenotypic distribution are favored in a particular environment, for example, selection will strongly favor insects that have very high resistance to an insecticide. In such cases, the type of selection that operates is ______ selection.
directional
If a high chi square value is obtained when comparing observed and expected genotypes in a population, we can state that the population is in
disequilibrium
A large, healthy, natural population typically exhibits a ______ level of SNPs.
high
Suppose a chi square analysis is performed to test whether the observed genotypes in a population are consistent with the predictions of Hardy-Weinberg equilibrium. Which type of chi square value will be obtained if a population is in disequilibrium?
high
During _____ gene transfer, genetic material from a donor organism is incorporated into a recipient organism which is not the donor's offspring.
horizontal
when two genetically related individuals mate its called _____. Unrelated individuals os known as _____.
inbreeding outbreeding
In a population that is undergoing directional selection, the mean fitness of the population ______.
increases with each generation
The mean fitness of a population undergoing directional selection is ______.
less than 1
The change in a population's gene pool from one generation to the next is known as ______.
microevolution
A _____ is any change in the DNA of an organism, for example, a change in DNA sequence or the structure and number of chromosomes.
mutation
Which of the following is an accurate depiction of the Hardy-Weinberg equation for a gene with two alleles?
p2 + 2pq + q2 = 1
Microevolution is best described as ______.
the change in a population's gene pool from generation to generation
Which of the following are required for gene flow to occur?
Migrants must be fertile and pass their genes to the next generation. Individuals must migrate from one population to another.
In population genetics, a gene that exists as two or more alleles in a population is a ______ gene, while one that exists predominantly as a single allele is a ______ gene.
polymorphic; monomorphic
When scientists study populations, they typically observe high levels of variation in many of the traits that characterize a species. In genetics, variations in traits at the population level are known as ______.
polymorphisms
The field of _____ genetics studies the extent of genetic variation within groups of people over time.
population
Which field of genetics would study the extent of genetic variation within groups of people over time?
population genetics
In _____ assortative mating, individuals tend to choose mates with with similar phenotypes. In _____ assortative mating, individuals tend to choose mates with dissimilar phenotypes.
positive negative