1) Which of the following is the best modern definition of evolution?
A) descent with modification
B) change in the number of genes in a population over time
C) survival of the fittest
D) inheritance of acquired characters
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A) descent with modification
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Natural selection acts on individuals, but
Example of this concept
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but only populations evolve
The finch population evolved by natural selection
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Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?
A) Each bird evolved a deeper, stronger beak as the drought persisted.
B) Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
C) Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in the previous generation.
D) The frequency of the strong-beak alleles increased in each bird as the drought persisted
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B) Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
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Microevolution
3 mechanisms of this concept
Only natural selection causes
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is a change in allele frequencies in a population over generations
Natural selection
Genetic drift
Gene flow
adaptive evolution
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prerequisite for evolution
Mendel's work on pea plants provided
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varitions in heritable traits
evidence of discrete heritable units (genes)
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Genetic variation among individuals is caused by
Phenotype is the product of
Natural selection can only act on variation with
Some phenotypic differences are determined by
Other phenotypic differences are determined by
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differences in genes or other DNA segments
inherited genotype and environmental influences
a genetic component
a single gene and can be classified on an either-or basis
the influence of two or more genes and vary along a continuum within a population
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Genetic variation can be measured as
For gene variability, average heterozygosity measures
Nucleotide variability is measured by
Nucleotide variation rarely results in
Some phenotypic variation (does not, but rather from)
Only genetically determined variation can have
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gene variability or nucleotide variability
the average percent of loci that are heterozygous in a population
comparing the DNA sequences of pairs of individuals
phenotypic variation
does not result from genetic differences among individuals, but rather from environmental influences
evolutionary consequences
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Genetic variation _____.
A) is created by the direct action of natural selection
B) arises in response to changes in the environment
C) must be present in a population before natural selection can act upon the population
D) tends to be reduced by when diploid organisms produce gametes
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C) must be present in a population before natural selection can act upon the population
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New genes and alleles can arise by
Sexual reproduction can result in genetic variation by
A mutation is
Only mutations in cells that
A point mutation is
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mutation or gene duplication
recombining existing alleles
a random change in nucleotide sequence of DNA
produce gametes can be passed to offspring
a change in one base in a gene
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The effects of point mutations can vary (5)
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Mutations that result in a change in protein production are often harmful
Harmful mutations can be hidden from selection in recessive alleles
Mutations that result in a change in protein production can sometimes be beneficial
Point mutations in noncoding regions generally result in neutral variation, conferring no selective advantage or disadvantage
Mutations to genes can be neutral because of redundancy in the genetic code
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Chromosomal mutations that (3)
Duplication of small pieces of DNA
Mutation rates are low in
The average is about
Mutation rates are often lower in ____________ and higher in _____________
Mutations accumulate quickly in
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delete, disrupt, or rearrange many loci are typically harmful
increases genome size and is usually less harmful
animals and plant
one mutation in every 100,000 genes per generation
prokaryotes, and viruses
prokaryotes and viruses because they have short generation times
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Sexual reproduction can
In organisms that reproduce sexually, recombination of alleles is
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shuffle existing alleles into new combinations
more important than mutation in producing the genetic differences that make adaptation possible
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population
gene pool
A locus is fixed if
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a localized group of individuals capable of interbreeding and producing fertile offspring
consists of all the alleles for all loci in a population
all individuals in a population are homozygous for the same allele
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Calculating Frequencies:
For diploid organisms
The total number of dominant alleles at a locus is
By convention, if there are two alleles at a locus
(examples of the math for frequencies on slide 37/38)
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the total number of alleles at a locus is the total number of individuals times 2
two alleles for each homozygous dominant individual plus one allele for each heterozygous individual; the same logic applies for recessive alleles
, p and q are used to represent their frequencies
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The Hardy-Weinberg equation describes
If the observed genetic makeup of the population differs from expectations under Hardy-Weinberg, it suggests
In a population where gametes contribute to the next generation randomly and Mendelian inheritance occurs, allele and genotype frequencies
This poulation is said to be in
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the genetic makeup we expect for a population that is not evolving at a particular locus
that the population may be evolving
remain constant from generation to generation
Hardy-Weinberg equilibrium
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Hardy-Weinberg equilibrium describes the
The Hardy-Weinberg theorem describes a
In real populations, allele and genotype frequencies
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constant frequency of alleles in such a gene pool
hypothetical population that is not evolving
do change over time
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The five conditions for nonevolving populations are rarely met in nature
Natural populations can
We can assume the locus that causes phenylketonuria (PKU) is in
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No mutations
Random mating
No natural selection
Extremely large population size
No gene flow
evolve at some loci, while being in Hardy-Weinberg equilibrium at other loci
Hardy-Weinberg equilibrium given that all 5 conditions are met
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In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because _____.
A) the population is diploid
B) heterozygotes can come about in two ways
C) the population is doubling in number
D) heterozygotes have two alleles
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B) heterozygotes can come about in two ways
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Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?
A) f(A1) = 0.9997, f(A2) = 0.0003
B) f(A1) = 0.9800, f(A2) = 0.0200
C) f(A1) = 0.9700, f(A2) = 0.0300
D) f(A1) = 0.9604, f(A2) = 0.0392
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C) f(A1) = 0.9700, f(A2) = 0.0300
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Three major factors alter allele frequencies and bring about most evolutionary change
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Natural selection
Genetic drift
Gene flow
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Natural Selection:
Differential success in reproduction results in
For example, an allele that confers resistance to DDT in fruit flies increased in frequency after
Natural selection can cause ___________ ________________ (define)
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certain alleles being passed to the next generation in greater proportions
DDT was used widely in agriculture
adaptive evolution, an improvement in the match between organisms and their environment
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Genetic Drift:
The smaller a sample, the greater the chance of
Genetic drift describes how
Genetic drift tends to reduce
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random deviation from a predicted result
allele frequencies fluctuate unpredictably from one generation to the next
genetic variation through losses of alleles
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The founder effect occurs when
Allele frequencies in the small founder population can be
The bottleneck effect is
The resulting gene pool may no longer be reflective of
If the population remains small
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a few individuals become isolated from a larger population
different from those in the larger parent population
a sudden reduction in population size due to a change in the environment
the original population's gene pool
it may be further affected by genetic drift
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Genetic drift is significant
Genetic drift can cause
Genetic drift can lead
Genetic drift can cause
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in small populations
allele frequencies to change at random
to a loss of genetic variation within populations
harmful alleles to become fixed
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Gene flow consists of
Alleles can be transferred through
Gene flow tends to
Gene flow can decrease
Example
Gene flow can increase
Example
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the movement of alleles among populations
the movement of fertile individuals or gametes (for example, pollen)
reduce variation among populations over time
the fitness of a population
Ex:the great tit (Parus major) on the Dutch island of Vieland
the spread of alleles for resistance to insecticides
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Evolution by natural selection involves both
New genetic variations arise by
Beneficial alleles are
Only natural selection consistently increases the
Natural selection brings about adaptive evolution by
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chance and "sorting"
chance
"sorted" and favored by natural selection
frequencies of alleles that provide reproductive advantage
acting on an organism's phenotype
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Relative Fitness:
The phrases "struggle for existence" and "survival of the fittest" are misleading as they imply
Relative fitness is the
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direct competition among individuals
contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
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Directional selection
Disruptive selection
Stabilizing selection
Striking adaptations by natural
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favors individuals at one extreme end of the phenotypic range
favors individuals at both extremes of the phenotypic range
favors intermediate variants and acts against extreme phenotypes
octopuses can change color rapidly for camo; jaws of snakes allow them to swallow prey larger than their heads
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Natural selection increases
Adaptive evolution occurs as
Because the environment can change
Genetic drift and gene flow do not consistently lead to adaptive evolution as they
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the frequencies of alleles that enhance survival and reproduction
the match between a species and its environment increases
adaptive evolution is a continuous process
can increase or decrease the match between an organism and its environment
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Sexual selection is
It can result in sexual dimorphism
IntrAsexual selection is
IntErsexual selection, often called mate choice, occurs when
Male showiness due to mate choice can
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natural selection for mating success
marked differences between the sexes in secondary sexual characteristics
is direct competition among individuals of one sex (often males) for mates of the opposite sex
individuals of one sex (usually females) are choosy in selecting their mates
increase a male's chances of attracting a female, while decreasing his chances of survival
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The "good genes" hypothesis suggests
Diploidy maintains genetic variation in the form of
Balancing selection occurs when
BS includes (2)
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if a trait is related to male genetic quality or health, both the male trait and female preference for that trait should increase in frequency
recessive alleles hidden from selection in heterozygotes
natural selection maintains stable frequencies of two or more phenotypic forms in a population
Heterozygote advantage
Frequency-dependent selection
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Heterozygote advantage occurs when
Natural selection will tend to
Heterozygote advantage can result from
A mutation in an allele that codes for part of the hemoglobin protein causes
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heterozygotes have a higher fitness than do both homozygotes
maintain two or more alleles at that locus
stabilizing or directional selection
sickle-cell disease, but also confers malaria resistance
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In frequency-dependent selection, the fitness of a phenotype
Selection favors whichever phenotype is
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declines if it becomes too common in the population
less common in a population
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Why Natural Selection Cannot Fashion Perfect Organisms:
selection can
evolution is
adaptations are
chance,
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act only on existing variations
limited by historical constraints
often compromised
natural selection, and the enviroment interact
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The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including those in their original homeland. Which of the following likely explains the genetic uniqueness of this population?
A) population bottleneck and Hardy-Weinberg equilibrium
B) heterozygote advantage and stabilizing selection
C) mutation and natural selection
D) founder effect and genetic drift
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D) founder effect and genetic drift
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An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?
A) directional selection
B) disruptive selection
C) a founder event
D) a genetic bottleneck
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D.a genetic bottleneck
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Which of the following is the most predictable outcome of increased gene flow between two populations?
A) lower average fitness in both populations
B) higher average fitness in both populations
C) increased genetic difference between the two populations
D) decreased genetic difference between the two populations
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D) decreased genetic difference between the two populations
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Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.
A) nonrandom mating
B) geographic isolation
C) genetic drift
D) gene flow
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D. gene flow
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Currently the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferably catch and eat slower iguanas are introduced to the island, iguana body size is likely to _____ in the absence of other factors; the iguanas would then be under _____ selection.
A) increase; directional
B) increase; disruptive
C) decrease; directional
D) decrease; disruptive
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C) decrease; directional
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