PCB 3044
PCB 3044 Exam 2 Review (Cook) 2026
How does hunting affect natural populations? What is trophy hunting, and how
does this change the genetic makeup of the population offspring? What affect
has this had on the ram? What has happened to maturation time in cod? Why?
-One way hunting affects natural populations is by causing evolutionary change.
-Trophy hunting is hunting for sport and displaying parts of an animal as
trophies. Trophy hunting causes the genetic characteristics of a population to
change, or evolve.
-This means rams with small horns are able to reproduce more frequently than
rams with bighorns, resulting in more small horn rams.
-In cod fishery, harvesting practices have selected individuals that mature at a
younger age and a smaller size for production purposes.
Define evolution. Explain using gene frequency. What is required of a trait for
natural selection to act upon it?
-We can define evolution as change over time in the frequencies (proportions) of
different alleles in a population.
-Gene frequency is the relative frequency of an allele at a particular locus in a
population, expressed as a fraction or percentage. A species evolves when gene
frequency changes over time.
-For natural selection to act upon a trait, the trait must possess heritable
variation and confer an advantage for the population.
What do genes code for? What are alleles? How is this related to genotype? If
allele frequencies change for a gene in a population, what can be said about that
gene?
-Genes specify how to build (encode) proteins.
-Alleles are one of two forms of a gene that result in the production of different
versions of the protein that the gene encodes.
PCB 3044
,PCB 3044
-Genotype is the genetic makeup of an individual. If a gene has two alleles,
designated A and a, the individual could be of genotype AA, Aa, or aa.
-If the frequency of the a allele were to change over time, from 40% to 71%,
then the population would have evolved at that gene.
Explain descent with modification using natural selection. What is a vestigial
structure, and how does this support the idea of descent with modification?
-Descent with modification is the idea that a species change over time, give rise
to new species, and share a common ancestor.
-A vestigial structure is a feature a species inherited from an ancestor but is now
less elaborate and functional than in the ancestor. This is an example of descent
with modification.
Describe why two populations might begin to develop different characteristics.
What factors would cause this?
-Darwin argued that is two populations experience different environmental
conditions, individuals with one set of characteristics may be favored by natural
selection in one population, while individuals with a different set of
characteristics may be favored in the other population.
What is a phenotype? What is it based off of? What causes phenotypes to vary?
-A phenotype is the observable characteristics of an organism, such as size or
color.
-The phenotype of an organism is influenced by its genes.
-Individuals differ from one another, in part because they have different alleles
of genes that influence their phenotype.
How do new alleles arise? Is this common?
-New alleles arise by mutation, a change in the DNA of a gene.
-Mutations are extremely rare.
What is recombination? How does it act upon mutation?
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,PCB 3044
-Recombination is the rearrangement of genetic material during sexual
reproduction that produces offspring with combinations of alleles that differ
from those in either of their parents.
-We can think of mutation as providing raw material (new alleles) on which
evolution is based, and recombination as rearranging that raw materials into
unique new combinations.
What are the three types of natural selection?
a. What is it called when one phenotypic extreme is favored?
b. What is it called when individuals of the intermediate phenotype are favored?
c. What is it called when phenotypes of two extremes are favored?
d. Sketch a graph of each type.
-The three types of natural selection are:
a. Directional selection occurs when individuals with one extreme of a heritable
phenotypic trait (e.g., large size) are favored over other individuals (small and
medium-sized individuals).
b. Stabilizing selection, when individuals with an intermediate phenotype (e.g.,
medium-sized individuals) are favored.
c. Disruptive selection, when individuals with a phenotype at either extreme are
favored (e.g., small and large individuals have an advantage over medium-sized
individuals).
-Graphs are in Concept 6.2 (Interactive Figure 6.6)
What is genetic drift? Is genetic drift an example of natural selection? What
types of populations are more impacted by genetic drift?
-Genetic drift is when random events affect which alleles are passed from one
generation to the next. It is greater in smaller populations than in large ones.
-Genetic drift is not an example of natural selection, it happens through an
PCB 3044
, PCB 3044
entirely random process.
-Small populations are more impacted by genetic drift.
What four possible effects can genetic drift have on a population?
a. What is fixation? How does this affect the genetic variation of a population?
b. Why can only mildly deleterious effects increase via genetic drift and not
terribly deleterious ones? (Hint: What effect might a terribly deleterious allele
have an organism's ability to reproduce? Are allele frequencies still based on
random chance in this case?)
c. How can genetic drift increase genetic differences between populations?
-Four possible effects of genetic drift on a population:
1. Can cause allele frequencies to fluctuate randomly over time in small
populations. Eventually, some alleles disappear from small populations, while
others reach fixation.
2. Genetic drift reduces the population's genetic variation, making the
individuals within the population more similar genetically to one another.
3. Genetic drift can increase the frequency of a harmful allele.
4. Genetic drift can increase genetic differences between populations because
random events may cause an allele to reach fixation in one population yet be
lost from another population.
-Fixation is when an allele occurs in a population at a frequency of 100%.
Fixation causes low genetic variation in a population.
-Genetic drift can "overrule" the effects of natural selection, causing a harmful
allele to randomly increase or decrease in frequency.
- Genetic drift can increase genetic differences between populations because
random events may cause an allele to reach fixation in one population yet be
lost from another population.
PCB 3044
PCB 3044 Exam 2 Review (Cook) 2026
How does hunting affect natural populations? What is trophy hunting, and how
does this change the genetic makeup of the population offspring? What affect
has this had on the ram? What has happened to maturation time in cod? Why?
-One way hunting affects natural populations is by causing evolutionary change.
-Trophy hunting is hunting for sport and displaying parts of an animal as
trophies. Trophy hunting causes the genetic characteristics of a population to
change, or evolve.
-This means rams with small horns are able to reproduce more frequently than
rams with bighorns, resulting in more small horn rams.
-In cod fishery, harvesting practices have selected individuals that mature at a
younger age and a smaller size for production purposes.
Define evolution. Explain using gene frequency. What is required of a trait for
natural selection to act upon it?
-We can define evolution as change over time in the frequencies (proportions) of
different alleles in a population.
-Gene frequency is the relative frequency of an allele at a particular locus in a
population, expressed as a fraction or percentage. A species evolves when gene
frequency changes over time.
-For natural selection to act upon a trait, the trait must possess heritable
variation and confer an advantage for the population.
What do genes code for? What are alleles? How is this related to genotype? If
allele frequencies change for a gene in a population, what can be said about that
gene?
-Genes specify how to build (encode) proteins.
-Alleles are one of two forms of a gene that result in the production of different
versions of the protein that the gene encodes.
PCB 3044
,PCB 3044
-Genotype is the genetic makeup of an individual. If a gene has two alleles,
designated A and a, the individual could be of genotype AA, Aa, or aa.
-If the frequency of the a allele were to change over time, from 40% to 71%,
then the population would have evolved at that gene.
Explain descent with modification using natural selection. What is a vestigial
structure, and how does this support the idea of descent with modification?
-Descent with modification is the idea that a species change over time, give rise
to new species, and share a common ancestor.
-A vestigial structure is a feature a species inherited from an ancestor but is now
less elaborate and functional than in the ancestor. This is an example of descent
with modification.
Describe why two populations might begin to develop different characteristics.
What factors would cause this?
-Darwin argued that is two populations experience different environmental
conditions, individuals with one set of characteristics may be favored by natural
selection in one population, while individuals with a different set of
characteristics may be favored in the other population.
What is a phenotype? What is it based off of? What causes phenotypes to vary?
-A phenotype is the observable characteristics of an organism, such as size or
color.
-The phenotype of an organism is influenced by its genes.
-Individuals differ from one another, in part because they have different alleles
of genes that influence their phenotype.
How do new alleles arise? Is this common?
-New alleles arise by mutation, a change in the DNA of a gene.
-Mutations are extremely rare.
What is recombination? How does it act upon mutation?
PCB 3044
,PCB 3044
-Recombination is the rearrangement of genetic material during sexual
reproduction that produces offspring with combinations of alleles that differ
from those in either of their parents.
-We can think of mutation as providing raw material (new alleles) on which
evolution is based, and recombination as rearranging that raw materials into
unique new combinations.
What are the three types of natural selection?
a. What is it called when one phenotypic extreme is favored?
b. What is it called when individuals of the intermediate phenotype are favored?
c. What is it called when phenotypes of two extremes are favored?
d. Sketch a graph of each type.
-The three types of natural selection are:
a. Directional selection occurs when individuals with one extreme of a heritable
phenotypic trait (e.g., large size) are favored over other individuals (small and
medium-sized individuals).
b. Stabilizing selection, when individuals with an intermediate phenotype (e.g.,
medium-sized individuals) are favored.
c. Disruptive selection, when individuals with a phenotype at either extreme are
favored (e.g., small and large individuals have an advantage over medium-sized
individuals).
-Graphs are in Concept 6.2 (Interactive Figure 6.6)
What is genetic drift? Is genetic drift an example of natural selection? What
types of populations are more impacted by genetic drift?
-Genetic drift is when random events affect which alleles are passed from one
generation to the next. It is greater in smaller populations than in large ones.
-Genetic drift is not an example of natural selection, it happens through an
PCB 3044
, PCB 3044
entirely random process.
-Small populations are more impacted by genetic drift.
What four possible effects can genetic drift have on a population?
a. What is fixation? How does this affect the genetic variation of a population?
b. Why can only mildly deleterious effects increase via genetic drift and not
terribly deleterious ones? (Hint: What effect might a terribly deleterious allele
have an organism's ability to reproduce? Are allele frequencies still based on
random chance in this case?)
c. How can genetic drift increase genetic differences between populations?
-Four possible effects of genetic drift on a population:
1. Can cause allele frequencies to fluctuate randomly over time in small
populations. Eventually, some alleles disappear from small populations, while
others reach fixation.
2. Genetic drift reduces the population's genetic variation, making the
individuals within the population more similar genetically to one another.
3. Genetic drift can increase the frequency of a harmful allele.
4. Genetic drift can increase genetic differences between populations because
random events may cause an allele to reach fixation in one population yet be
lost from another population.
-Fixation is when an allele occurs in a population at a frequency of 100%.
Fixation causes low genetic variation in a population.
-Genetic drift can "overrule" the effects of natural selection, causing a harmful
allele to randomly increase or decrease in frequency.
- Genetic drift can increase genetic differences between populations because
random events may cause an allele to reach fixation in one population yet be
lost from another population.
PCB 3044
