PCB 3044
PCB 3044 Exam 2 Study Questions and
Answers Graded A+ 2026
Genotype
The genetic makeup of an individual
Evolution
Change in allele frequencies in a population over time
Descent with modification
Passing traits from parent to offspring
As a population accumulates differences over time and a new species forms, it is
different from its ancestors
But the new species shares many of the same characteristics as its ancestors and
resembles them
Natural selection
Individuals with certain heritable traits survive and reproduce more successfully
than other individuals.
Individuals with __________ traits have more offspring, and their alleles will
___________ in frequency in the population.
Favored; increase
Phenotype
Observable characteristics that are determined by the genotype
Mutation
A change in dna of a gene. Mutation provides the raw material on which evolution
is based
Recombination
The rearrangement of genetic material, especially by crossing over in
chromosomes or by the artificial joining of segments of dna from different
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,PCB 3044
organisms. Also produce different genotypes within a population. Recombination
rearranges the raw material into new combinations.
Types of natural selection
Directional selection, stabilizing selection and disruptive selection
Directional selection
Individuals at one phenotypic extreme are favored ex. Drought favored large beak
size in medium ground finches
Stabilizing selection
Individuals with an intermediate phenotype are favored ex. Parasitic wasps of
eurosta fly select for larvae in small gall size; while birds select for eurosta larvae
in large gall
Disruptive selection
Individuals at both phenotypic extremes are favored ex. African seedcrackers
(birds) have two food sources
Genetic drift
Occurs when chance events determine which alleles are passed to the next
generation. It is significant only for small populations
Genetic drift has four effects on evolution in small populations
1. It acts by chance alone, thus causing allele frequencies to fluctuate at random.
Some alleles may disappear, others may reach 100% frequency (fixation).
2. Because some alleles are lost, genetic variation of the population is reduced.
3. Frequency of harmful alleles can increase if the alleles have only mildly
deleterious effects.
4. Differences between populations can increase. Chance events may lead to allele
fixation in one population and loss from another population.
Gene flow
Alleles move between populations via movement of individuals or gametes
Gene flow has two effects
1. Populations become more similar genetically
2. New alleles can be introduced into a population
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, PCB 3044
Natural selection is the only evolutionary mechanism that consistently causes
_____________ _________
Adaptive evolution
Adaptations
Improve the ability to survive and reproduce. This include morphological and
physiological features
Adaptive evolution
Process by which traits that confer advantages in survival or reproduction tend to
increase in frequency over time
Examples of rapid adaptive evolution:
1. Antibiotic resistance in bacteria
2. Insecticide resistance in insects
Clines
Patterns of change in a characteritic over a geographic region
Phenotypic plasticity
One genotype may produce different phenotypes under different environmental
conditions.
Lack of genetic variation
If there is no beneficial allele, adaptive evolution at that gene cannot occur ex.
Initially, mosquito populations lacked alleles for pesticide resistance so the
pesticides were effective. Advantageous alleles arise by chance.
Evolutionary history
Natural selection works on/modifies traits that already exist. Organisms have
certain characteristics and lack others because of their ancestry. Ex: dolphins
evolved from terrestrial mammals; they have lungs and cannot "breathe"
underwater.
Ecological trade-offs
PCB 3044
PCB 3044 Exam 2 Study Questions and
Answers Graded A+ 2026
Genotype
The genetic makeup of an individual
Evolution
Change in allele frequencies in a population over time
Descent with modification
Passing traits from parent to offspring
As a population accumulates differences over time and a new species forms, it is
different from its ancestors
But the new species shares many of the same characteristics as its ancestors and
resembles them
Natural selection
Individuals with certain heritable traits survive and reproduce more successfully
than other individuals.
Individuals with __________ traits have more offspring, and their alleles will
___________ in frequency in the population.
Favored; increase
Phenotype
Observable characteristics that are determined by the genotype
Mutation
A change in dna of a gene. Mutation provides the raw material on which evolution
is based
Recombination
The rearrangement of genetic material, especially by crossing over in
chromosomes or by the artificial joining of segments of dna from different
PCB 3044
,PCB 3044
organisms. Also produce different genotypes within a population. Recombination
rearranges the raw material into new combinations.
Types of natural selection
Directional selection, stabilizing selection and disruptive selection
Directional selection
Individuals at one phenotypic extreme are favored ex. Drought favored large beak
size in medium ground finches
Stabilizing selection
Individuals with an intermediate phenotype are favored ex. Parasitic wasps of
eurosta fly select for larvae in small gall size; while birds select for eurosta larvae
in large gall
Disruptive selection
Individuals at both phenotypic extremes are favored ex. African seedcrackers
(birds) have two food sources
Genetic drift
Occurs when chance events determine which alleles are passed to the next
generation. It is significant only for small populations
Genetic drift has four effects on evolution in small populations
1. It acts by chance alone, thus causing allele frequencies to fluctuate at random.
Some alleles may disappear, others may reach 100% frequency (fixation).
2. Because some alleles are lost, genetic variation of the population is reduced.
3. Frequency of harmful alleles can increase if the alleles have only mildly
deleterious effects.
4. Differences between populations can increase. Chance events may lead to allele
fixation in one population and loss from another population.
Gene flow
Alleles move between populations via movement of individuals or gametes
Gene flow has two effects
1. Populations become more similar genetically
2. New alleles can be introduced into a population
PCB 3044
, PCB 3044
Natural selection is the only evolutionary mechanism that consistently causes
_____________ _________
Adaptive evolution
Adaptations
Improve the ability to survive and reproduce. This include morphological and
physiological features
Adaptive evolution
Process by which traits that confer advantages in survival or reproduction tend to
increase in frequency over time
Examples of rapid adaptive evolution:
1. Antibiotic resistance in bacteria
2. Insecticide resistance in insects
Clines
Patterns of change in a characteritic over a geographic region
Phenotypic plasticity
One genotype may produce different phenotypes under different environmental
conditions.
Lack of genetic variation
If there is no beneficial allele, adaptive evolution at that gene cannot occur ex.
Initially, mosquito populations lacked alleles for pesticide resistance so the
pesticides were effective. Advantageous alleles arise by chance.
Evolutionary history
Natural selection works on/modifies traits that already exist. Organisms have
certain characteristics and lack others because of their ancestry. Ex: dolphins
evolved from terrestrial mammals; they have lungs and cannot "breathe"
underwater.
Ecological trade-offs
PCB 3044
