Genetics Ch23
Population
A group of individuals of the same species, which occupy the same region, and can successfully interbreed with each other, is a(n) ________ of that sexually reproducing species.
quantitative traits that are influenced by more than one gene
Disruptive selection typically acts on ______.
In two or more alleles are maintained in a heterogeneous environment
In disruptive selection, ______.
changes in genetic variation within a group of individuals over time
Population genetics is a field that is concerned with ______.
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.
G - 0.20; g - 0.80
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?
A - 0.48; a - 0.52
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 expected frequencies of the two alleles after one generation?
drift
Any random change in the frequencies of alleles in a population is referred to as genetic _______.
the maintenance of two or more alleles in a population
Balancing selection favors ______.
disequilibrium
Fill in the blank question. 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
random change of allele frequencies
Genetic drift is the ______ in a population.
selection coefficient
Genotypes that have lower relative fitnesses are selected against. The extent of that selection is measured by s, the _____ _____.
Yes, stabilizing selection tends to decrease the genetic diversity of those genes.
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?
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?
do not change
The Hardy-Weinberg equilibrium is a mathematical expression, which predicts that, when certain requirements are met, the allele and genotype frequencies of a gene in a population ______ over the course of many generations.
Mutations have a negligible effect on allelic frequencies, while mechanisms such as natural selection and drift can have a dramatic effect.
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?
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?
stabilizing selection
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?
Population 1 is more susceptible.
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?
A = 0.58; a = 0.42
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?
directional selections
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?
The mean fitness of the population will increase.
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)?
10
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?
beneficial
According to the principles of natural selection, a mutant allele will increase in the population if it is ______ to reproduction and survival.
0.8
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?
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.
How is the allele frequency of a population calculated?
Alleles are either lost (frequency of 0%) or fixed (frequency of 100%) in the populations.
If genetic drift is followed over a great many generations, what is its expected effect on allele frequencies?
gene pool
The ______ of a population consists of all of the alleles of every gene in all of the individuals of that population.
mean fitness
The ______ of a population is the sum of the frequencies of all genotypes, each one multiplied by its respective relative fitness.
microevolution
The change in a population's gene pool from one generation to the next is known as ______.
Population
The field that studies the extent of genetic variation within groups of people over time is called __________ genetics.
less than 1
The mean fitness of a population undergoing directional selection is ______.
natural selection
The mechanism of evolution through _______ ___________was proposed by Charles Darwin and Russel Wallace in the 1850s.
natural selection
The mechanism of evolution through ________ _________ states that those individuals better adapted to their environment are more likely to survive and reproduce.
Darwinian fitness
The relative likelihood that a genotype will contribute its alleles to the next generation, as compared to other genotypes, is known as _________ ________.
Stabilizing
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.
They are under stabilizing selection, which should decrease their genetic diversity.
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?
the extent to which a genotype is selected against
What does the selection coefficient measure?
p2 + 2pq + q2 = 1
Which of the following is an accurate depiction of the Hardy-Weinberg equation for a gene with two alleles? Multiple choice question.
The Michigan population likely experienced a bottleneck in the past. Both populations are equally susceptible to genetic drift.
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?
genotype; DD genotype
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 ______.
allele; p allele
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 ______.
- No new mutations in the Col gene. -Animals in the population mate randomly, regardless of their genotype for the Col gene -There is no natural selection.
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.
all of the alleles of every gene that were passed from the 60 parents to the 48 new cubs
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?
The number of individuals with this genotype in the population is divided by the total number of individuals in the population.
How can we calculate the frequency of a specific genotype in a population?
balancing
Natural selection favors the maintenance of two or more alleles in a population in balancing ________ selection. An example of that is the phenomenon of heterozygote advantage.
Disruptive
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.
evolutionary change is not occurring in this population
The Hardy-Weinberg equilibrium is used as a null hypothesis, i.e., if a population is in Hardy-Weinberg equilibrium, then ______.
The heterozygous genotype (HbAHbS) is more resistant to malaria than either of the homozygous genotypes.
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?
polymorphisms
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 ______.
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.)
-Some genotypes are more likely to survive to reproductive age than others. -Some genotypes are more likely to find mates than others. -Some genotypes are more fertile than others.
Which of the following are likely reasons for differences in the reproductive success of different genotypes in a population?
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?
This gene is under balancing selection due to heterozygote advantage in those areas.
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?
a group of individuals that occupy the same area and can interbreed with each other
Which of the following correctly defines a population of sexually reproducing species for the purposes of population genetics?
sBBp = sbbq
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).
A new allele, which promotes higher fitness in organisms that carry it, is introduced in a population (for example, by a random mutation).
Which of the following is a situation in which directional selection may be observed?
Certain genotypes are more likely to continue to live after surviving to reproductive age.
Which of the following is not a reason for differences in the reproductive success of different genotypes in a population?
the relative likelihood that a genotype will contribute alleles to the next generation as compared to other genotypes
Which of the following is the best definition of Darwinian fitness as it relates to population genetics?
mutation
Which of the following phenomena is responsible for introducing new genetic variation in a population?
Natural selection favors individuals with a heterozygous genotype.
Which of the following would not be true for a population that is in Hardy-Weinberg equilibrium for a specific gene? Multiple choice question.
heterozygote advantage
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.
increases with each generation
In a population that is undergoing directional selection, the mean fitness of the population ______.
dd, wdd = 1.0
In a specific population, a gene is present as two alleles: D and d. For every 100 dd individuals 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.
negative frequency
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.
gametes are formed from alleles independently chosen at random from
In order to derive the Hardy-Weinberg equation, the two originators assumed that ______ the population's gene pool.
directional
Individuals at one extreme of a phenotypic distribution are more likely to survive and reproduce in a particular environment due to selection.
the change in a population's gene pool from generation to generation
Microevolution is best described as ______.
polymorphism
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.
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.
