ch 23 smart book
True or false: While horizontal gene transfer is very common between different species of bacteria, it cannot occur between different species of eukaryotes, or between eukaryotes and bacteria.
F
Which of the following formulas allows us to calculate the expected number of mutations in a gene in a population?
Expected number of new mutations = 2Nμ
Which of the following are likely reasons for
Some genotypes are more fertile than others. Some genotypes are more likely to survive to reproductive age than others. Some genotypes are more likely to find mates than others.
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.
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 fitness values 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 can microsatellites and minisatellites be used to determine the relatedness between individuals within a population?
The sizes of those repetitive sequences tend to be more similar in closely related individuals.
In disruptive selection, ______.
two or more alleles are maintained in a heterogeneous environment
A specific gene is found in two forms in a population, D and d, with frequencies of 0.6 and 0.4, respectively. The D allele can mutate into the d allele at a rate of 0.00001 mutations per gene per generation. What would the expected frequency of the d allele be after one generation? Assume that the reverse mutation d to D does not occur.
0.400006 Δp = (0.00001 x 0.6) = 0.000006, which is added to the value for q.
Gene B is found in two allelic forms in a population, B and b, each with a frequency of 0.5. The B allele can mutate into the b allele at a rate of 0.0001 mutations per gene per generation. What would the expected frequency of the B allele be after 100 generations? Assume that the reverse mutation from b to B does not occur.
0.495 Solve the equation: (1−0.0001)100 = pt/0.5
Which of the following is a situation in which directional selection may be observed? Multiple choice question.
A new allele, which promotes higher fitness in organisms that carry it, is introduced in a population (for example, by a random mutation).
If genetic drift is followed over a great many generations, what is its expected effect on allele frequencies?
Alleles are either lost (frequency of 0%) or fixed (frequency of 100%) in the populations.
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.
Which of the following best describes the relationship between a genotype's fitness and its frequency in negative frequency-dependent selection? Multiple choice question.
As the frequency of a genotype increases, its fitness decreases.
hen two genetically related individuals mate, it is called . In contrast, mating between unrelated individuals is known as .
Blank 1: inbreeding Blank 2: outbreeding
New mutations can be deleterious, neutral, or beneficial. Which of those three general types of mutations are most likely to occur? Multiple choice question.
Deleterious and neutral mutations are much more likely than beneficial mutations.
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 are required for gene flow to occur?
Individuals must migrate from one population to another. Migrants must be fertile and pass their genes to the next generation.
Which of the following is a similarity between microsatellites and minisatellites?
They consist of many tandem repeats of a certain DNA sequence
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
assortative
Horizontal gene transfer (HGT) between different species of bacteria is relatively common. Scientists estimate that about ______ of the genetic variation between modern bacteria can be attributed to HGT.
20-30%
You are studying a gene with two alleles, A and a, in a population of plants. The relative fitness coefficients of the three genotypes for this gene are as follows: wAA = 0.5; wAa = 1; waa = 0.3. If this population is undergoing balancing selection due to heterozygote advantage, what would the expected equilibrium frequencies of A and a be? Multiple choice question.
A = 0.58; a = 0.42 p = Allele frequency of A = Saa / SAA + Saa. Thus, 0.7 / 0.5 + 0.7 = 0.58. Frequency for aa = 1 − frequency for AA. 1 − 0.58 = 0.42.
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.
Blank 1: assortative
Individuals tend to choose mates with similar phenotypes in _______assortative mating. In ____ assortative mating, individuals tend to choose mates with dissimilar phenotypes.
Blank 1: positive or +
Individuals tend to choose mates with similar phenotypes in __assortative mating. In ___assortative mating, individuals tend to choose mates with dissimilar phenotypes.
Blank 1: positive or + Blank 2: negative or -
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.
Reproduction between two genetically related individuals, such as cousins, is called
Inbreeding
Which of the following is a major disadvantage of inbreeding in natural populations?
Inbreeding lowers the mean fitness of a population when homozygotes have a lower relative fitness value.
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? Multiple choice question.
Population 1 is more susceptible.
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 following accurately describes these two populations?
The Michigan population likely experienced a bottleneck in the past. Both populations are equally susceptible to genetic drift.
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 fitness values 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)? Multiple choice question.
The mean fitness of the population will increase.
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.
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? Multiple choice question.
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? Multiple choice question.
Stabilizing selection typically acts on quantitative traits determined by multiple genes. Does stabilizing selection have an effect on the genetic diversity of those genes and if so, what type of effect? Multiple choice question.
Yes, stabilizing selection tends to decrease the genetic diversity of those genes.
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
Natural selection favors the maintenance of two or more alleles in _____ a population in selection. An example of that is the phenomenon of heterozygote advantage.
balancing
Why are repetitive sequences, such as microsatellites and minisatellites, an extremely useful tool for studying population genetics?
because they tend to exhibit considerable variation between individuals
Most mutations are ______.
deleterious or neutral
Sometimes, a population can experience high levels of inbreeding if the population's size has been reduced for some reason. This can lead to lower reproductive success, causing an even larger decrease in the population's size, a phenomenon known as inbreeding
depression
Individuals at one extreme of a phenotypic distribution are more likely to survive and reproduce in a particular environment due to ______ selection.
directional
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
Some traits are quantitative, i.e., they are determined by multiple genes and exhibit a range of phenotypes. For some of those traits, the fitness values for particular genotypes may be higher in one environment and lower in another. When populations with such traits inhabit heterogeneous environments, multiple alleles can be maintained through the action of ______ selection. Multiple choice question.
disruptive
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
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? Multiple choice question.
disruptive selection
Any random change in the frequencies of alleles in a population is referred to as genetic
drift
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 est
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 effect
Which of the following mutations are likely to cause a defective protein to be made?
frameshift mutation missense mutation nonsense mutation
When individuals migrate, alleles can be transferred from one population to another population. This is commonly referred to as
gene flow
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 homozygous 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 homozygous genotypes, we are observing a situation called ______. (Assume that it is a single gene with two alleles.)
heterozygote advantage
Inbreeding is useful in agriculture because it can result in a high proportion of ______.
homozygotes that exhibit a trait that is of interest to a breeder
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 ______ of a population is the sum of the frequencies of all genotypes, each one multiplied by its respective relative fitness.
mean fitness
Any change in the DNA of an organism, for example, a change in DNA sequence or the structure and number of chromosomes is called a(n)
mutation
The type of selection that acts on quantitative traits determined by multiple genes is selection. In this type of _______ selection, individuals with intermediate phenotypes have higher fitness and are selected for, while extreme phenotypes are selected against.
stabilizing
What does the selection coefficient measure? Multiple choice question.
the extent to which a genotype is selected against ; equal to one minus the fitness value.
Balancing selection favors ______.
the maintenance of two or more alleles in a population
A population of small insects consists of 500,000 individuals. The mutation rate for a gene in this species is 0.00001 mutations per gene per generation. What is the expected number of new mutations in this population in the next generation?
10
Which of the following is a typical mutation rate (with proper units) for a gene in a natural population? Multiple choice question.
10−6 per gene per generation
A population is undergoing a directional selection for a gene with two alleles, allele A has a frequency of 0.4, and allele a has a frequency of 0.6. The relative fitness values for the three genotypes are as follows: wAA = 1, wAa = 0.5, and waa = 0.5. What would be the e
A - 0.48; a - 0.52 First, you have to calculate the mean fitness of the population. Once you have that, calculate the frequencies of genotypes in the next generation by taking the Hardy-Weinberg predicted formula, multiplying them by the relative fitness and dividing by the mean fitness. For example, for the AA genotype, you would calculate p2wAA/(mean fitness). After you have calculated the expected genotype frequencies, calculate the allele frequencies.
The weight of a human baby at birth is a quantitative trait determined by the activity of many genes. Babies with very low or very high birth weights have a decreased chance of survival, while babies with intermediate birth weights have much better chances of survival. What can you hypothesize about the genetic diversity of genes that determine birth weight in humans?
They are under stabilizing selection, which should decrease their genetic diversity.
Genetic material from a donor organism is incorporated into a recipient organism which is not the donor's offspring during ___gene transfer.
horizontal
The transfer of genetic material from one species to another (regardless of the exact mechanism) is called ______.
horizontal gene transfer
A short tandem repeat (STR), or ______, is a type of repetitive sequence which is less than two hundred base pairs in length and for which the unit that repeats is about 1-6 bp long. In contrast, ______ are 1-20 kbp long and are composed of a unit that is 6-80 base pairs long.
microsatellite; minisatellites
Which of the following phenomena is responsible for introducing new genetic variation in a population?
mutation
Which of the following would be a neutral mutation?
mutation of a sequence within an intron change in the wobble position without affecting the amino acid sequence of the encoded protein missense mutation that causes an amino acid substitution which does not affect the proper folding of the protein
in disruptive selection, ______.
two or more alleles are maintained in a heterogeneous environment
Which of the following is the best definition of Darwinian fitness as it relates to population genetics?
the relative likelihood that a genotype will contribute alleles to the next generation as compared to other genotypes
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
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? Multiple choice question.
−0.05
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 allow free movement of frogs between ponds. Which of the following accurately describes differences in allele frequencies between different ponds within each area? Multiple choice question.
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.
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 calc
frequency of D in the donor population proportion of the conglomerate population that is due to migrants from the donor population frequency of D in the original recipient population
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
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.
proportion of the conglomerate population that is due to migrants from the donor population frequency of D in the original recipient population frequency of D in the donor population
Disruptive selection typically acts on ______.
quantitative traits that are influenced by more than one gene
Genetic drift is the ______ in a population.
random change of allele frequencies
The probability that a gene will be altered as a result of mutation is known as the mutation
rate
A gene is present in a population in two forms. The frequency of allele G is 0.3, while the frequency of allele g is 0.7. The most fit genotype is gg, with a relative fitness of 1. The relative fitness of the heterozygotes is 0.6, and that of the dominant homozygotes is 0.3. In this case of directional selection (which favors the g allele), what would the frequencies of the two alleles (G and g) be after one generation? Multiple choice question.
G - 0.20; g - 0.80 First, you have to calculate the mean fitness of the population. Once you have that, calculate the frequencies of genotypes in the next generation by taking the Hardy-Weinberg predicted formula, multiplying them by the relative fitness and dividing by the mean fitness. For example, for the GG genotype, you would calculate p2wGG/(mean fitness). After you have calculated the expected genotype frequencies, calculate the allele frequencies.
Most eukaryotic species contain short sequences, typically a few base pairs to a few thousand base pairs long, that are repeated many times throughout the genome. The general name for these types of sequences is ______ sequences. Multiple choice question.
repetitive
Which of the following formulas describe the situation in which a population undergoing balancing selection due to heterozygote advantage reaches equilibrium? In this case, we have a single gene, with two alleles, B and b, with frequencies of p (for the B allele) and q (for the b allele). Multiple choice question.
sBBp = sbbq
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 ____, Incorrect Unavailable, but may also involve the structure and number of chromosomes.
sequences
