BIOL 240 Final Exam Week 4 LO with
questions and well verified answers actual
exam!!! 2026
population - ANSWER -A group of individuals of the same species living in the same
geographic area at the same time who can interbreed and produce fertile offspring.
gene pool - ANSWER -The complete set of all alleles for all genes present in a population
at a given time. The gene pool describes the total genetic diversity available within a
population.
smallest unit of evolution - ANSWER -The POPULATION is the smallest unit of evolution
— not the individual. Individual organisms do not evolve; their genotype is fixed at conception.
Evolution is a change in allele frequencies in a population over time.
MECHANISMS OF EVOLUTION — Genetic Drift - ANSWER -Random changes in allele
frequencies due to chance sampling events, not natural selection. Has the greatest effect in
SMALL populations. Tends to reduce genetic variation over time. Can cause alleles to become
fixed (frequency = 1.0) or lost (frequency = 0) entirely by chance. Does not result in adaptation.
MECHANISMS OF EVOLUTION — Founder Effect - ANSWER -A type of genetic drift that
occurs when a small group of individuals breaks away from a larger population and establishes
a new population. The founders carry only a subset of the original gene pool, so the new
population may have very different allele frequencies — including high frequencies of rare
alleles if a founder happened to carry them. Reduces genetic diversity. Example: high
frequency of certain genetic disorders in isolated religious communities (e.g., Ellis-van Creveld
syndrome in the Amish).
MECHANISMS OF EVOLUTION — Bottleneck Effect - ANSWER -A type of genetic drift that
occurs when a population is drastically reduced in size due to a catastrophic event (disease,
natural disaster, hunting). The surviving population's gene pool is a random, reduced sample of
, the original. Allele frequencies shift randomly; many alleles may be lost entirely. Example:
cheetahs have extremely low genetic diversity due to a past population bottleneck; northern
elephant seals were hunted nearly to extinction and now show very low genetic diversity.
MECHANISMS OF EVOLUTION — Gene Flow - ANSWER -The movement of alleles into or
out of a population due to migration of individuals (or gametes, like pollen). Immigration ADDS
new alleles to a population; emigration REMOVES alleles. Tends to make neighboring
populations more similar to each other over time. Reduces genetic differences between
populations. Can introduce new alleles that natural selection or drift then act upon.
MECHANISMS OF EVOLUTION — Natural Selection - ANSWER -Differential survival and
reproduction of individuals based on heritable traits. Individuals with traits better suited to the
environment survive and reproduce more → their alleles increase in frequency over
generations. Only mechanism that consistently leads to adaptation. Requires heritable
variation and differential reproductive success.
NATURAL SELECTION — Directional Selection - ANSWER -Selection favors one extreme
phenotype over the other(s). The distribution of phenotypes shifts toward the favored
extreme. One allele increases in frequency; the other decreases. Example: antibiotic resistance
in bacteria — bacteria with resistance alleles survive and reproduce; sensitive bacteria die.
Example: increase in average beak size in birds when only large seeds are available.
NATURAL SELECTION — Disruptive Selection - ANSWER -Selection favors BOTH extreme
phenotypes over the intermediate phenotype. The population splits toward two extremes. Can
lead to two distinct phenotypic classes and may eventually drive speciation. Example: black
and white oyster catchers (birds) — both dark and light morphs survive better than
intermediate forms in different microhabitats; medium birds survive poorly in both.
NATURAL SELECTION — Stabilizing Selection - ANSWER -Selection favors the
INTERMEDIATE phenotype and acts against both extremes. Reduces variation; keeps the
population centered on the current optimal phenotype. Most common type of selection in
stable environments. Example: human birth weight — babies of intermediate weight survive
best; very small and very large babies have higher mortality. Example: clutch size in birds —
too few or too many eggs both reduce fitness.
MUTATIONS AND EVOLUTION - ANSWER -Mutations are the ULTIMATE source of all new
genetic variation — they are the raw material for evolution. Mutations alone are typically too
rare and random to shift allele frequencies significantly in the short term. Most mutations are
neutral or slightly harmful; very few are beneficial. However, beneficial mutations in a given
environment can be acted upon by natural selection and increase in frequency over time.
questions and well verified answers actual
exam!!! 2026
population - ANSWER -A group of individuals of the same species living in the same
geographic area at the same time who can interbreed and produce fertile offspring.
gene pool - ANSWER -The complete set of all alleles for all genes present in a population
at a given time. The gene pool describes the total genetic diversity available within a
population.
smallest unit of evolution - ANSWER -The POPULATION is the smallest unit of evolution
— not the individual. Individual organisms do not evolve; their genotype is fixed at conception.
Evolution is a change in allele frequencies in a population over time.
MECHANISMS OF EVOLUTION — Genetic Drift - ANSWER -Random changes in allele
frequencies due to chance sampling events, not natural selection. Has the greatest effect in
SMALL populations. Tends to reduce genetic variation over time. Can cause alleles to become
fixed (frequency = 1.0) or lost (frequency = 0) entirely by chance. Does not result in adaptation.
MECHANISMS OF EVOLUTION — Founder Effect - ANSWER -A type of genetic drift that
occurs when a small group of individuals breaks away from a larger population and establishes
a new population. The founders carry only a subset of the original gene pool, so the new
population may have very different allele frequencies — including high frequencies of rare
alleles if a founder happened to carry them. Reduces genetic diversity. Example: high
frequency of certain genetic disorders in isolated religious communities (e.g., Ellis-van Creveld
syndrome in the Amish).
MECHANISMS OF EVOLUTION — Bottleneck Effect - ANSWER -A type of genetic drift that
occurs when a population is drastically reduced in size due to a catastrophic event (disease,
natural disaster, hunting). The surviving population's gene pool is a random, reduced sample of
, the original. Allele frequencies shift randomly; many alleles may be lost entirely. Example:
cheetahs have extremely low genetic diversity due to a past population bottleneck; northern
elephant seals were hunted nearly to extinction and now show very low genetic diversity.
MECHANISMS OF EVOLUTION — Gene Flow - ANSWER -The movement of alleles into or
out of a population due to migration of individuals (or gametes, like pollen). Immigration ADDS
new alleles to a population; emigration REMOVES alleles. Tends to make neighboring
populations more similar to each other over time. Reduces genetic differences between
populations. Can introduce new alleles that natural selection or drift then act upon.
MECHANISMS OF EVOLUTION — Natural Selection - ANSWER -Differential survival and
reproduction of individuals based on heritable traits. Individuals with traits better suited to the
environment survive and reproduce more → their alleles increase in frequency over
generations. Only mechanism that consistently leads to adaptation. Requires heritable
variation and differential reproductive success.
NATURAL SELECTION — Directional Selection - ANSWER -Selection favors one extreme
phenotype over the other(s). The distribution of phenotypes shifts toward the favored
extreme. One allele increases in frequency; the other decreases. Example: antibiotic resistance
in bacteria — bacteria with resistance alleles survive and reproduce; sensitive bacteria die.
Example: increase in average beak size in birds when only large seeds are available.
NATURAL SELECTION — Disruptive Selection - ANSWER -Selection favors BOTH extreme
phenotypes over the intermediate phenotype. The population splits toward two extremes. Can
lead to two distinct phenotypic classes and may eventually drive speciation. Example: black
and white oyster catchers (birds) — both dark and light morphs survive better than
intermediate forms in different microhabitats; medium birds survive poorly in both.
NATURAL SELECTION — Stabilizing Selection - ANSWER -Selection favors the
INTERMEDIATE phenotype and acts against both extremes. Reduces variation; keeps the
population centered on the current optimal phenotype. Most common type of selection in
stable environments. Example: human birth weight — babies of intermediate weight survive
best; very small and very large babies have higher mortality. Example: clutch size in birds —
too few or too many eggs both reduce fitness.
MUTATIONS AND EVOLUTION - ANSWER -Mutations are the ULTIMATE source of all new
genetic variation — they are the raw material for evolution. Mutations alone are typically too
rare and random to shift allele frequencies significantly in the short term. Most mutations are
neutral or slightly harmful; very few are beneficial. However, beneficial mutations in a given
environment can be acted upon by natural selection and increase in frequency over time.
