Chapter 19 (Part 2): How Population Change Overtimee
Which of the following is an example of stabilizing selection? - Newborn babies of intermediate weight are most likely to survive; both high and low birthweights are associated with increased infant mortality. - A population of finches that colonizes an island where large seeds are abundant experiences a gradual increase in beak size over many generations. - In a varied environment, squirrels with dark fur and squirrels with very light fur are favored, but squirrels with intermediate coloration are not.
- Newborn babies of intermediate weight are most likely to survive; both high and low birthweights are associated with increased infant mortality.
For a gene with two alleles, S and s, if the frequency of the one allele (S) is 0.25, then the frequency of the other allele(s) is
.75
The MN blood group in humans is determined by two alleles of a single gene. In a population containing 90 individuals with genotype MM and blood group M, 80 individuals with genotype MN and blood group MN, and 30 individuals with genotype NN and blood group N, what is the frequency of the genotype MN?
0.40 add 90+30+80 = 200 80/200=0.40
Consider a population of 100 four o'clock flowers, where 55 flowers are red and have the genotype C^RC^R, 20 flowers are pink and have the genotype C^RC^W, and 25 flowers are white with the genotype C^WC^W. The frequency of the C^R allele in this population is _______________
0.65/65%/(130/200)/13:20 20+2(55) 2(55)+2(20)+2(25)
In a diploid species, how many copies of a given allele are present in an individual who is heterozygous for the gene?
1
A diploid homozygous individual has ______ copies of the given allele.
2
You are conducting an experiment to measure the effect of a fertilizer on plant growth. You measure the height of plants treated with the fertilizer and control plants that are not treated. Which of the following data sets would have the smallest random sampling error associated with it?
500 plants Reason: The smallest sample size will have the largest sampling error.
Which of the following statements is true of a gene subject to diversifying selection?
A genotype that has high fitness in one environment has low fitness in a different environment.
What is a gene pool?
All of the alleles for every gene in a population
What phenotypes are favored by Balancing selection?
An array of polymorphic genotypes
Which of the following is an example of directional selection? -In colonial bentgrass, plants are highly sensitive to metal or highly resistant to metal; intermediate phenotypes are rarely observed. -An increase in the number of mice with brown fur compared to the number of mice with white fur. -Most human infants have a birth weight close to the mean of the population; very high and very low weights are both uncommon.
An increase in the number of mice with brown fur compared to the number of mice with white fur.
Select the types of selection that tend to increase or maintain genetic diversity within a population. Stabilizing Selection Balancing selection Disruptive selection Directional Selection
Balancing selection Disruptive selection
Which type of selection favors individuals at one extreme of a phenotypic range who have greater reproductive success in a particular environment?
Directional Selection
A starting population of light fur mice has a mutation that produces a brown colored mouse. This gives it a selective reproductive advantage because it less susceptible to predation and can reproduce more frequently than the light colored mice. Over many generations there is a selection for the darker colored mouse. This is an example of which of the following?
Directional selection
In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?
Directional selection
What type of selection can cause a favored allele to predominate in a population?
Directional selection
What type of selection favors the survival of two or more different genotypes that produce different phenotypes?
Diversifying selection
Which type of natural selection selects for two different phenotypes, each of which is most fit in a particular environment?
Diversifying selection
What phenotypes are favored by stabilizing selection?
Intermediate phenotypes
How does stabilizing selection affect genetic diversity within a population?
It tends to decrease genetic diversity.
What are possible outcomes of genetic drift?
Loss of an allele Fixation of an allele
If directional selection favors a homozygous genotype, then what long-term result can occur?
Monomorphic gene
What phenotypes are favored by Disruptive selection?
Multiple different extreme phenotypes
What types of genotypes are favored by diversifying selection?
Multiple different genotypes that produce different phenotypes
What is the process by which beneficial traits that are heritable become more common in successive generations?
Natural Selection
What phenotypes are favored by directional selection?
One extreme of a phenotypic range
In radishes, genotype RR is red, genotype Rr is purple, and genotype rr is white. In a population of radishes consisting of 100 red radishes, 100 purple radishes, and 300 white radishes, what is the frequency of the genotype rr?
Reason: The frequency of the r allele is (300 + 300 + 100) / (500 X 2), which is 0.70. However, this question asks for the frequency of the rr genotype, which is 300/500, or 0.60.
A particular gene segregates two alleles, and the dominant allele has a frequency of 0.9. What is the frequency of the recessive allele?
Reason: The sum of the two allele frequencies is 1.0. Therefore, 1.0 - 0.9 = 0.1.
Variation in fitness is due to the fact that some genotypes have greater _______________ success than other genotypes in a population.
Reproductive
Why does genetic drift affect small populations more strongly than it affects large populations?
Small populations are more likely to be affected by sampling errors.
This graph represents the number of eggs per nest (x-axis) versus the number of nests with a given number of eggs (y-axis) before and after selection. The change in this population is best explained by a pattern of natural selection called _______________ selections
Stabilizing
In which of the following patterns of natural selection are the extremes of a phenotypic distribution selected against?
Stabilizing selection
Which type of selection favors individuals with intermediate phenotypes and selects against individuals with extreme phenotypes?
Stabilizing selection
What type of traits does sexual selection tend to favor?
Traits that increase an individual's ability to find a mate and mate successfully
An allele frequency describes the frequency at which a particular _______________ occurs within a population.
allele
The term microevolution describes changes in
allele frequencies from generation to generation.
Which type of selection tends to maintain genetic diversity within a population?
balancing Selection
In negative frequency-dependent selection, the fitness of a genotype ______ when its frequency becomes higher.
decreases
This graph represents changes in the frequencies of fur color in mice that occurred over many generations after a mutation causing darker fur arose in the population. The change in this population is best explained by _______________ selection
directional
Among a population of finches, beak size is either very small or very large; intermediate beak sizes are rarely observed. This is best explained by ______ selection.
diversifying
Under a model of ______ selection, a genotype that has high fitness in one environment is likely to have low fitness in a second environment; however, a different genotype in the same population is likely to have low fitness in the first environment and high fitness in the second environment.
diversifying
The existence of both metal-resistant and metal-sensitive alleles in this population of grasses is an example of _______________ selection due to heterogeneous environments.
diversifying or disruptive
This is a graphical representation of:
diversifying selection
Genetic drift can lead to the __________ or __________ of alleles in a population.
elimination/loss/decrease/removal/deletion fixation/increase/fix/addition/stabilazation
A prolonged change in the ______ can initiate directional selection because the new conditions may favor one genotype and promote elimination of the others.
environment
In four-o'clock plants, flowers with the genotype CRCR are red, flowers with the genotype CRCW are pink, and flowers with the genotype CWCW are white. A population of four-o'clocks consists of 30 plants with red flowers, 10 plants with pink flowers, and 60 plants with white flowers. What is the frequency of the CR allele in this population?
f(C^R) = ([30x2] + [10x1])/(100x2) = 0.35
True or false: Due to genetic drift, alleles with high fitness tend to become fixed in populations, and alleles with lower fitness tend to become lost.
false
diversifying selection
favors both extreme phenotypes but selects against intermediate phenotypes
balancing selection
favors heterozygosity, or can favor the uncommon allele
directional selection
favors one extreme phenotype
stabilizing selection
favors the intermediate phenotype
A variation in ______ occurs when some genotypes result in greater reproductive success than other genotypes.
fitness
The _______________ _______________ of a population consists of all of the alleles for every gene in the population.
gene; pool
What term describes changes in allele frequencies within a population over time due to random chance?
genetic drift
The frequency at which homozygotes and heterozygotes occur within a population can be described by:
genotype frequencies
The number of individuals with a particular genotype in a population divided by the total number of individuals in a population is the:
genotype frequency
The genotype frequency is calculated by dividing the number of individuals in a population who have a particular ______ by the total number of ______ in that population
genotype; individuals
Because migration leads to gene flow, it tends to ______ genetic diversity within populations.
increase
For a trait subject to stabilizing selection, individuals with ______ have the highest fitness.
intermediate phenotypes
Migration increases genetic diversity within populations because it
introduces new alleles into the population.
Stabilizing selection tends to decrease genetic diversity because
it eliminates alleles that cause extreme phenotypes.
Sampling error tends to be small when the sample size is
large
Balancing selection tends to ______ by favoring maintenance of two or more alleles, even if one of the alleles results in lower fitness.
maintain genetic diversity
Changes in the gene pool of a population from generation to generation are called
microevolution
By an evolutionary mechanism called _______________ _______________, individuals with heritable, favorable traits have increased survival and reproduction, and the traits become more common in the population.
natural selection
If individuals with rare phenotypic variants tend to have the highest fitness for a particular trait, the trait is likely subject to
negative frequency-dependent selection.
Genetic drift selects for
no particular allele
When mating is _______________, individuals choose their mates based on similar phenotype, dissimilar phenotype, or genetic lineage.
nonrandom
Individuals who choose mates depending on phenotypic similarity or genetic relatedness are experiencing
nonrandom mating.
For a gene with two alleles, if the frequency of one allele in a population that is not evolving is symbolized p and the frequency of the other allele in the population is symbolized q, then
p + q = 1.
A set of individuals of the same species inhabiting the same environment at the same time make up a
population
A(n) _______________ is a group of individuals of the same species that occupy the same environment and can interbreed with one another.
population
What is genetic drift?
random change in allele frequency
What type of selection affects traits that directly influence an individual's ability to mate successfully?
sexual selection
Birds that lay intermediate numbers of eggs have greater fitness than birds that lay either too many or too few eggs. This is an example of
stabilizing selection.
Environmental changes can lead to directional selection because they cause changes in
the relative fitness of various genotypes.
