Genetics Ch 23

You are studying two populations of the same species. Population A consists of 100 individuals, while population B consists of 1,000 individuals. Which of the two populations will have (1) a higher number of new mutations appearing in the next generation, and which population will have (2) a higher likelihood of fixation of new mutations?

(1) - population B, (2) - population A

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

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

The Old Order Amish of Lancaster County, Pennsylvania were founded by only three couples in the 1700. Currently, this human population is made of thousands of people. Which of the following is a characteristic of this population nowadays, that is a consequence of the founder effect in this population's history?

A much higher frequency of certain very rare human genetic diseases

Arrange the principles of natural selection in the order in which they occur, with the first step at the top.

A mutation occurs Individuals with the mutation are more likely to reproduce Over the course of many generations, frequency of mutation increases

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 all the genes that were passed from the 60 parents to the 48 new cubs

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.

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

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 certain populations, natural selection can favor the maintenance of 2 or more alleles in a population. An example of this is

Balancing selection

Why are repetitive sequences, such as micro and minisatellites an extremely useful tool for studying population genetics?

Because they tend to exhibit considerable variation between individuals

According to the principles of natural selection, a mutant allele will increase in the population if it is ______ to reproduction and survival.

Beneficial

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.

In a natural setting, migration between two populations usually occurs in a bidirectional manner (some individuals of each population migrate to the other population). What is the consequence of such bi-directional movement on allele frequencies in the two populations?

Differences in allele frequencies are reduced.

In ___ selection, individuals at one extreme of a phenotypic distribution are more likely to survive and reproduce in a particular environment.

Directional

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.

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 these situations, an equilibrium is reached, in which both alleles of the gene are maintained in the population.

Heterozygote Advantage

During ___ gene transfer, genetic material from a donor organism is incorporated into a recipient organism which is not the donor's offspring.

Horizontal

Sometimes, both alleles of a gene in a particular individual are identical because they were actually descended from the same common ancestor. The probability of that occurring is called the ___ coefficient.

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.

Why is inbreeding useful in agriculture?

It can result in a high proportion of homozygotes that exhibit a trait that is of interest to a breeder.

The mean fitness of a population undergoing directional selection is

Less than 1

Within a large populations, smaller groups who may be separated from other groups by geographic barriers and whose members are likely to interbreed with each other form a ______ population.

Local

Choose all that is 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.

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 Animals in the population mate randomly, regardless of their genotype for the Col gene No natural selection

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.

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 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.

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 drift. In which of the two populations will it take fewer generations for a new allele to be fixed?

Population A

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 survive to reproductive age than others. Some genotypes are more likely to find mates than others. Some genotypes are more fertile than others.

___ 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

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.

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 homozygote 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.

Which of the following best defines the inbreeding coefficient?

The probability that two identical alleles in an individual are descended from the same common ancestor.

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

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.

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.

The ___ effect is observed when a population's size is dramatically reduced due to natural events, such as earthquakes and flood, or due to human destruction of habitat.

bottleneck

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

diversifying selection.

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

do not change over the course of many generations.

The term genetic ___ refers to any random change in the frequencies of alleles in a population.

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.

In DNA ___, an individual is characterized based on the repetitive sequences in his or her genome.

fingerprinting

Which of the following is an accurate depiction of the Hardy-Weinberg equation for a gene with two alleles?

p2 + 2pq + q2 = 1

In population genetics, a gene that exists as two or more alleles in a population is a(n) ______ gene, while one that exists predominantly as a single allele is a(n) ______ gene.

polymorphic; monomorphic

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

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.

Disruptive selection typically acts on

quantitative traits that are influenced by more than one gene.

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

GG genotype.

When individuals migrate, alleles can be transfered from one population to another population. This commonly referred to as ___ ___.

Gene flow

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

Human individuals can be characterized by analyzing the presence and sizes of repetitive sequences in their DNA, a technique known as

DNA fingerprinting.

How can DNA fingerprinting be used to determine if a natural population is undergoing inbreeding depression?

DNA fingerprints can be used to determine the degree of relatedness between the population's members.

Which of the following phenomena is responsible for introducing new genetic variation in a population?

Mutation

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.

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

Directional Selection

You are studying two areas inhabited by a species of frog. In area X, ponds inhabited by the frogs are less frequent 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.

Two types of factors can govern microevolution. On one hand, mutation is a constant source of new genetic variation. On the other hand, mechanisms, 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.

The mechanism of evolution through ___ ___ states that those individuals better adapted to their environment are more likely to survive and reproduce.

Natural Selection

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.

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?

Yes, stabilizing selection tends to decrease the genetic diversity of those genes.

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.

The ______ of a population consists of all of the alleles of every gene in all of the individuals of that population.

gene pool

DNA fingerprinting can be used to determine the relationship between humans (for example paternity) because closely related individuals, such as a father and his child

have more similar DNA fingerprints than do more distantly related individuals.

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 ______ of a population is the sum of the frequencies of all genotypes, each one multiplied by its respective relative fitness.

mean fitness

The mechanism of evolution through ___ ___ was proposed by Charles Darwin and Russel Wallace in the 1850s.

natural selection

A change in one nucleotide in a gene is also known as a ___ nucleotide ___, or, SNP.

single-nucleotide polymorphism

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

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

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

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 bottleneck effect.

Genetic drift is

the random change of allele frequencies in a population.

In disruptive selection,

two or more alleles are maintained in a heterogeneous environment.

Order the events that a population undergoing inbreeding depression might experience, starting at the top.

1. Population size is dramatically reduced 2. Population experiences high level of inbreeding 3. Mean fitness decreases 4. Population decreases even more, possible extinction

The transfer of genetic material from one species to another (regardless of the exact mechanism) is called

horizontal gene transfer.

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 founder effect.

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

The change in a population's gene pool from one generation to the next is known as

Microevolution

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.

.32

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.

How can micro 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.

A large, healthy, natural population typically exhibits

a high level of SNPs

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

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.

The human population known as the Old Order Amish of Lancaster County exhibits an unusually high frequency of the genetic disease Ellis-van Creveld syndrome. What explains that observation?

This population was founded by a very small group of people.

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

repetitive sequences.

The Hardy -Weinberg equilibrium is used as a null hypothesis, i.e., if a population is in Hardy-Weinberg equilibrium, then

evolutionary change is not occurring in this population.