Biology 106 Chapter 20: Genes Within Population
Consider a population with 100 cats. If 72 cats are black and 28 are white, what is the phenotypic frequency of black cats?
0.72
The most fit phenotype is assigned a fitness value of ______.
1
__________ selection is a process that can lead to change, and __________ is the outcome or record of change over time.
Blank 1: Natural Blank 2: evolution
In general, ________ are more likely to exhibit mate choice than ________.
Blank 1: female Blank 2: male
Which of the following statements about intrasexual selection (assume males are the competing sex) is true?
Often a few successful males may engage in an inordinate number of matings, while most males do not mate at all.
What is gene flow?
The movement of alleles into or out of a population.
The phenotype frequency is calculated by dividing the total number of individuals with a particular phenotype by which of the following?
The total number of individuals in that population
If the frequency of allele A is 0.6 and the frequency of allele a is 0.4, what is the probability that an individual will receive two a alleles?
0.16 0.4 = allele a = p 2 a alleles = p^2 p^2 = 0.16
You are examining allele frequencies of a gene in a population of frogs. This gene has two alleles, T and t. If the frequency of the dominant allele (T) is 0.25, then the frequency of the recessive allele (t) is
0.75, .75, or 75%
Select all of the following events that could lead to a population bottleneck.
A natural disaster such as an earthquake or flood Human destruction of habitat An infectious disease that kills a large proportion of the population
Which evolutionary mechanism changes genotype frequencies but does not change allele frequencies?
Assortative mating
Which type of selection favors individuals at one extreme of a phenotypic range who have greater reproductive success in a particular environment?
Directional selection
What term quantifies reproductive success of a phenotype?
Fitness
Which of the following statements about the reproductive strategies of males and females is true?
Males and females often have different reproductive strategies.
In many species of animals, males and females look very different as a result of sexual selection. These animal species exhibit which of the following? Sexual dimorphism Sexual differentiation Sexual separation Sexual divergence
Sexual dimorphism
What is fitness?
The relative likelihood that a genotype will contribute to the gene pool of the next generation
What can likely happen to uncommon alleles in small, isolated populations as a result of genetic drift?
They are likely to be lost.
Select all of the following criteria that must be present for natural selection to occur and cause evolutionary change in a population.
Variation must have a genetic basis. Variation must result in differences in the number of offspring surviving in the next generation. Variation must exist among individuals.
A population bottleneck could be caused by
a natural disaster.
Natural selection results in ______ in a population.
adaptations
When researchers raised guppies in laboratory pools with high levels of predation, the guppies in those aquariums
became smaller and drab in coloration as a result of natural selection after about 10 generations.
Evolutionary change cannot occur in populations with no _________ variation.
genetic
Different alleles of genes are found within different individuals of a population. This is known as
genetic variation
Sexual selection influences
mating success. fitness. mate choice.
For a gene with two alleles, what equation represents the sum of all gene frequencies?
p + q = 1
Which of the following is not a direct benefit of mate choice?
A healthier male is less likely to carry disease.
Which of the following is true of evolutionary forces in natural populations?
Evolutionary forces can alter allele frequencies in natural populations
Many 19th century scientists believed that natural selection always favored an optimal form, and therefore would tend to reduce or eliminate which of the following?
genetic variation
For a gene with two alleles, B and b whose frequencies are p and q respectively, the probability that an individual receives a B allele from its mother and a B allele from its father is which of the following?
p^2
What evolutionary mechanism results in random changes in allele frequencies from one generation to the next?
Genetic drift
How does genetic drift affect allele frequencies in a population?
It changes allele frequencies without regard for their fitness.
How does gene flow affect allele frequencies among populations?
It tends to decrease differences in allele frequencies.
Which evolutionary mechanism causes beneficial traits that are heritable to become more common in a population?
Natural selection
Natural selection is expected to counter the effects of genetic drift when which condition is met?
Populations are very large.
Assortative mating changes ________ frequencies but does not change ________ frequencies.
genotype; allele
The amount of genetic variation present in naturally occurring populations is
significant.
Select all of the following that could cause evolutionary change by natural selection.
A moth that has a gene for cryptic coloration A plant with an enzyme that makes it disease-resistant
True or false: Within the same species, females and males usually employ the same reproductive strategy.
False
How does natural selection affect allele frequencies?
It causes beneficial alleles to become more common. It causes detrimental alleles to become less common.
Natural selection results in a population better adapted to its environment because
Natural selection results in a population better adapted to its environment because
Select the conditions that must be met for a population to be in Hardy-Weinberg equilibrium.
No new mutations occur. Mating is random. The population is very large.
If we find evidence that a population is experiencing changes in allele frequencies from one generation to the next, we say that this population is which of the following? In Hardy-Weinberg equilibrium Not in Hardy-Weinberg equilibrium Increasing in size Not evolving
Not in Hardy-Weinberg equilibrium
In Northeastern South America, which of the following is the main predator in streams found just below waterfalls?
Pike cichlids
Which describes male guppies located below South American waterfalls where predation is high?
They exhibit drab coloration.
The number of copies of an allele in a population divided by the total number of all alleles for that gene in a population is the
allele frequency.
The bottleneck effect occurs when allele frequencies change due to
an event that drastically reduces population size.
In many animals, selection has favored traits that confer greater ability in mate competition; as a result of such selection, one of the sexes —usually males—can look very different. This is known as sexual ______.
dimorphism
In theory, if mutation rates were high enough, alleles could be maintained in a population
even if the alleles are not favored by natural selection.
Natural selection can lead to ________ if variation is genetically based.
evolution
Genetic variation is necessary for _________ change to occur.
evolutionary
Promoting or constraining evolutionary change via the movement of beneficial or detrimental alleles into or out of a population is an effect of
gene flow.
Some genes can affect multiple aspects of an organism's phenotype. This phenomenon is known as __________.
pleiotropy
In chickens, the same gene that affects a hen's comb also affects the rate at which the hen lays eggs. This is an example of
pleiotropy.
Gene flow may (choose all that apply) maintain Hardy-Weinberg conditions. reduce evolutionary change. promote evolutionary change. introduce new alleles to a population. remove alleles from a population.
reduce evolutionary change. promote evolutionary change. introduce new alleles to a population. remove alleles from a population.
For a gene with two alleles whose frequencies are p and q, the Hardy-Weinberg equation states that the genotypes that are possible for the population are p^2 + 2pq + q^2, which is equal to
(p + q)^2.
Regarding a particular trait in a population of painted turtles (Chrysemys picta), 14% of the turtles have the homozygous dominant genotype, 70% are heterozygous, and 16% are homozygous recessive. What is the value of q^2?
0.16 Why? 16% = 0.16 homozygous recessive is q^2 (or bb) homozygous dominant is p^2 (or BB) heterozygous is 2pq (or Bb)
If the frequency of heterozygotes in a population of mice is 0.48 for a particular gene, what would be the frequency of heterozygotes in future generations if the population is in Hardy-Weinberg equilibrium?
0.48
In a population of seahorses, red seahorses on average produce 125 offspring and brown seahorses produce 75 offspring. What is the fitness of the brown phenotype?
0.6
Select all of the following that increase the chances of genetic drift in a population. Migration into a population occurs. A few individuals of a population become isolated. Only a few individuals contribute gametes to the next generation. Natural selection is acting upon the population. A population becomes very small.
A few individuals of a population become isolated. Only a few individuals contribute gametes to the next generation. A population becomes very small.
Select the types of large populations that are more likely to experience genetic drift.
A large population of garter snakes in which only a few individuals contribute to the next generation. A large population of garter snakes that started from a few individuals.
Which of the following are potential direct benefits of mate choice?
A male that provides the best parental care increases the chances of rearing more offspring. A male that has a better territory can provide higher quality food for females.
Select the observations that would indicate that a population is deviating from Hardy-Weinberg equilibrium.
Allele frequencies are changing between generations. Genotype frequencies do not match those predicated by the Hardy-Weinberg equation based on existing allele frequencies.
Why does selection occur?
Because some individuals in a population possess more favorable phenotypes than others.
What is the founder effect?
Changes in allele frequencies that result from the colonization of a new location by a small group of individuals from a larger population
Sexual selection is a type of natural selection in which the evolution of certain traits is driven by which of the following types of competition?
Competition for mates
Selection against intermediate-sized beaks in African black-bellied seedcracker finches is an example of which of the following? Disruptive selection Frequency-dependent selection Stabilizing selection Oscillating selection
Disruptive selection
Which type of selection acts to eliminate individuals which are intermediate on a phenotypic range?
Disruptive selection
Which of the following is a driving force of intersexual selection?
Female choice of males based on certain characteristics
How does genetic drift affect allele frequencies?
It changes allele frequencies randomly.
Consider population 1 in which the frequency of allele A = 0.1 and population 2 in which the frequency of allele A = 0.7. What will happen to the frequency of A in population 1 if individuals from population 2 move into population 1?
It will increase.
Which of the following is true about the reproductive strategies of males and females?
Males are selective in choosing a mate much less frequently than females.
What is genetic drift?
Random changes in the allele frequencies of a population over time
A deer's antlers, a ram's horns and the bright plumage of a male paradise bird are all examples of which of the following?
Secondary sexual characteristics
What type of selection affects traits that influence an individual's chances to find a mating partner or be chosen as a mating partner?
Sexual selection
__________ selection favors individuals with intermediate phenotypes and selects against individuals with extreme phenotypes.
Stabilizing or Stabilising
Which type of selection favors individuals with intermediate phenotypes and selects against individuals with extreme phenotypes?
Stabilizing selection
How can the founder effect cause a previously rare genetic disorder to become common in the new population?
The allele frequencies in the founding members of the population differ from the allele frequencies in the original large population.
How is the size of a population related to the likelihood that the population will experience genetic drift?
The larger the population, the lower the chance of genetic drift is.
In a laboratory experiment, researchers placed guppies in three different types of pools: no predation, low predation, and high predation. Researchers hypothesized that predation is a selective force and that large, brightly colored guppies are more conspicuous to predators. Based on that, what would you predict the guppies will look like in the pool with high predation after 10 generations?
They should be smaller and not very brightly colored
True or false: Genetic drift, mutations, and nonrandom mating are three agents that can act to produce evolutionary changes in a population.
True
The founder effect results in a new population which differs in ________ frequencies from its source population.
allele
Genetic variation in a population results from evolutionary forces that cause changes in
allele frequencies
Genetic ________ can likely play a role in large populations that were small at some point in their existence.
drift
In natural populations, most genes
exhibit variation
If a population is in Hardy-Weinberg equilibrium, the allele __________ of two alleles for a given trait can be calculated from the phenotypic frequencies.
frequencies
Which of the following agents of evolutionary change occurs when alleles move from one population to another?
gene flow
According to the theory of blending Inheritance, offspring were expected to be phenotypically ____________ relative to their parents, which would dilute any new genetic variants.
intermediate
A type of sexual selection in which members of one sex, usually females, choose mates based on particular characteristics such as courtship songs is called _______ _______.
intersexual selection
In ________ selection, a small number of males may mate an inordinate number of times, while a large number of males rarely mate if they mate at all.
intrasexual
What is the ultimate source of all new alleles?
mutation
Changes in allele frequencies within a population may result from __________, which are changes in the nucleotide sequences of an organism's DNA.
mutations
When a population is in Hardy-Weinberg equilibrium
no natural selection is occurring.
Features that increase the chance that a male will be chosen by a female (for example, bright plumage in many male birds) are known as _______ _______ characteristics.
secondary sexual
_______ selection is a type of natural selection in which competition for mates drives the evolution of certain traits.
sexual
Genetic drift is more likely to overwhelm natural selection when populations are ___________.
small
A dramatic reduction in population size due to a natural disaster or destruction of habitat and the resulting change in the allele frequencies of the new population is called
the bottleneck effect.
The change in allele frequencies that occur due to the colonization of a new location by a small group of individuals is called
the founder effect.
For a population to be in Hardy-Weinberg equilibrium,
there must be no migration into or out of the population.
Consider a gene in a population of fruit bats. There are two alleles for this gene, A and a, that occur in a population with the frequencies 0.8 and 0.2, respectively. If the population is in Hardy-Weinberg equilibrium, what genotype frequencies will be observed?
0.64 AA 0.32 Aa and 0.04 aa
For a gene with two alleles, A and a, with allele frequencies given by p and q respectively, identify the chance that an offspring will inherit the following combinations of alleles in a population that is in Hardy-Weinberg equilibrium.
AA = p^2 Aa = 2pq aa = q^2
Evolutionary change is not caused by phenotypic variation if the phenotypic variation lacks which of the following?
Genetic basis
Consider a gene with two alleles, one dominant, and the other recessive. If this population is in Hardy-Weinberg equilibrium with respect to this gene, what would happen to the dominant allele from generation to generation?
Its frequency would remain unchanged
__________ is the ultimate source of genetic variation.
Mutation
Select all of the following processes that can cause changes in allele or genotype frequencies in populations. Mutations Genetic drift Nonrandom Mating Random Mating Natural selection Gene flow
Mutations Genetic drift Nonrandom Mating Natural selection Gene flow
Evolution can result from any process that changes the ______ composition of a population.
genetic
In nature, mutation rates are usually ______ to maintain alleles that are not favored in a population by natural selection.
not high enough
Consider a gene that has 4 alleles in a particular population: F, M, S, and VS. What is the sum of all of the frequencies of all the alleles for this gene in that population?
one
Which is a correct version of the Hardy-Weinberg equation for genotype frequencies in a population in equilibrium?
p^2 + 2pq + q^2 = 1
