Evolution of Population Flashcards
What are the main mechanisms of evolutionary change?
Natural selection
Genetic drift
Gene flow
what is the modern synthesis
theory that reconciled Darwinian selection theory with Mendelian genetics to explain the origin of biological diversity
why doesn’t natural selection produce “perfect” organisms
- Selection can act ONLY on existing variations
- evolution is limited by historical constraints
- Adaptations often comprise
what is blended inheritance
what is the inheritance of acquired characters
why have notions of inheritance of acquired characters AND blended inheritance fallen into disfavor
what is Mendel’s contribution to genetics?
discovered the fundamental laws of inheritance
set the stage for understanding the genetic differences base of evolution
where does genetic variation come from
Mutations, Gene duplication and sexual reproduction
explain how heterozygote advantage maintains detrimental alleles (sickle cell anemia)
dominant allele protects them from a genetic disease, while their recessive allele protects them from an infectious disease
three ways sexual reproduction contributes to genetic variation
- crossing over
- an independent assortment of chromosomes
- fertilization
how would a point mutation FAIL to change the effect of a natural selection on an organism
Point mutations in noncoding regions commonly result in neutral variation (no advantage or disadvantage to organism)
how is the Hardy-Weinberg equation used to determine if a population is evolving
determines what the genetic makeup of a population would be if it’s NOT evolving at that locus and then compares it to the current population
what are the parts of the HW equation
P, PQ and Q
explain this statement :
“Mendelian processes alone DO NOT alter allele frequencies”
if these were the only processes at work then there would be no change to the allele frequency.
a common misconception about evolution
individual organisms evolve
even though natural selection acts on individuals the impact is ONLY seen
at the population level
what reduces genetic variation
population bottleneck
less genetic variation means there is
less opportunity for natural selection to adapt to environmental pressures
what is evolution on its smallest scale
microevolution
microevolution
changes in allele frequencies in a population over generations
TRue or false
natural selection is the ONLY cause of microevolution
FALSE
what is the mechanism to CONSISTENTLY improve the match of organisms and environment
natural selection
genetic drift
chance events that alter allele frequencies
gene flow
the transfer of alleles between populations
what is a prerequisite for mechanisms that cause allele frequency changes/evolution
genetic variation
what makes evolution possible
genetic variation
what didn’t Darwin know about organisms
HOW they pass heritable traits to their offspring
who set the stage for understanding the genetic differences of evolution
Mendel
True or False
Individuals in the same species will vary in phenotypic traits
TRUE
True or False
phenotypic variations DON’T reflect genetic variation
FALSE
how does phenotypic variation reflect genetic variation
differences among individuals in the composition of their genes or DNA sequences
what is suggested by heritable phenotypic differences occurring on an “either-or” basis
typically determined by a SINGLE gene locus with different alleles producing different phenotypes
what is suggested by phenotypic differences that vary along a continuum
result from influence of two or more gees on a single phenotypic character
Genetic variation at the whole-gene level can be quantified as the
the average percentage of loci that are heterozygous
Genetic variation at the molecular level of DNA has
very little variation resulting in phenotypic variation
why does genetic variation at the molecular level NOT result in phenotypic variation
Most of the variations occur in introns
what is phenotype a product of
inherited genotype and many environmental influences
what part of phenotypic variation can have evolutionary consequences
only genetically determined part
true or false
evolution can occur without genetic variation
FALSE
genetic variation evolution depends on
processes that produce new alleles and genes
true or false
sexual reproduction can also result in genetic variation
true
why can sexual reproduction result in genetic variation
genes are arranged in new ways
new alleles can arise from
mutations
mutations
change in the nucleotide sequence of an organism’s DNA
most NEW mutations that alter a phenotype are
at least slightly harmful
how can diploid organisms can hide harmful alleles
harmful alleles that are recessive can be hidden from selection by heterozygote protection
heterozygote protection
more favourable dominant allele can mask the recessive harmful one
True or false
a mutation can, on occasion, make its bearer better suited to the environment
TRUE
what is the ONLY way mutations can be passed to offspring in multicellular organisms
mutations in cell lines that produce gametes
what chromosomal changes are usually harmful
changes that delete, disrupt or rearrange
how can changes not affect phenotype
large scale changes that leave genes intact
key source of varaition
duplication of genes due to error in meiosis
example of how an error in meiosis cause variation
unequal crossing over
duplication of large chromosomal segments would be
harmful
duplications of smaller pieces of DNA may
not be harmful
what happens when mutations accumulate with gene duplications over generations with NO effects
expanded genome with new genes
mutations tend to be _____ in plants and animals
low
prokaryotes often have _____ number of mutations than plants and animals
lower
what is the link between more generations of time and mutations (prokaryotes)
mutations quickly generate genetic variation in populations
what type of genome has a higher mutation rate
RNA genome compared to the DNA genome
Most of the genetic variation in the population comes from
the unique combination of alleles each individual receives from parents
sexual reproduction shuffles ______ and deals them _______ to produce individual genotypes
existing alleles AND randomly
what is used to test whether a population is evolving
HW equation
does genetic variation guarantee that a population will evolve
NO
population
group of individuals of the same species living in the same area and interbreed
what does interbreeding cause
makes individuals more closely related to each other than those of another population
true of false
all populations are isolated/have sharp boundaries
FALSE
what can characterize a population’s genetic makeup
gene pool
the gene pool consists of
all copies of every type of allele at every locus in all members of the population
what does it mean if an allele is fixed in the gene pool
only one allele exists for a particular locus in a population
if an allele is fixed, than it must be
homozygous
what will a population look like if it’s NOT evolving
allele and genotype frequencies will remain constant from generation to generation
when is a population said to be in HW equilibrium
population is NOT evolving
HW principle considers
the combination of alleles in ALL of the crosses in a population
P2 in HW equilibrium
frequency of HOMOZYGOUS DOMINANT genotype
2pq
frequency of HETEROZYGOUS genotype
q2
frequency of HOMOZYGOUS RECESSIVE genotype
True or false
the population’s gene pool over the generations can change the frequency of one allele relative to another ALONE
FALSE
departure from the conditions for HW equilibrium can result in
evolutionary change
5 conditions for HW equilibrium
- no mutations
- random mating
- no gene flow
- no natural selection
- extreme large population sizes
what happens if there are mutations in HW equilibrium
gene pool is modified
what happens if there are no random matings in HW equilibrium
interbreeding/ choice breeding = random mixing of gametes DOESN’T occur and genotype frequencies change
what happens if there is natural selection in HW equilibrium
allele frequencies change when individuals with different genotypes show consistent differences in their survival/reproductive success
what happens if there are small population sizes in HW equilibrium
allele frequencies fluctuate by chance over time (genetic drift)
what happens if there is gene flow in HW equilibrium
gene flow can alter allele frequencies
natural selection is based on
differential success in survival and reproduction
adaptive evolution
traits that enhance survival or reproduction tend to increase in frequency over time
how can natural selection cause adaptive evolution
by consistently favouring some alleles over others
genetic drift is a major issue for _____ populations
small
two circumstances that can result in genetic drift having an impact on the population
- founder effect
- bottleneck effect
founder effect
When a few individuals become isolated from the larger population the smaller group may establish a new population with a gene pool that differs from the source population
what accounts for the high frequency of inherited disorders among isolated human populations
founder effect
bottleneck effect
sudden change in the environment can drastically reduce the size of a population
what happens to alleles when undergoing a bottleneck
they can be overrepresented, underrepresented or absent in the population
Genetic drift can cause allele frequencies to
change at random
how is genetic drift different from natural selection
Unlike natural selection which consistently favours some alleles over others, genetic drift causes allele frequencies to change at random over time
Genetic drift can lead to loss of
genetic variation in populations
Genetic drift can cause harmful alleles to
become fixed
Gene flow
transfer of alleles into or out of a population because of the movement of fertile individuals or their gametes
true of false
gene flow can reduce genetic differences between populations
TRUE
only mechanism that consistently causes adaptive evolution
natural selection
is the outcome of natural selection random
NO
what are ideas about relative fitness that are MISLEADING
Suggestions to mean a direct competitive contests among individuals
Relative fitness
The contribution an individual makes to the gene pool of the next generation is RELATIVE to the contributions of other individuals
selections in relative fitness are more directly on the ______ than the ____
phenotype AND genotype
Three ways natural selection can alter the frequency of distribution of heritable traits based on what phenotypes favoured
- directional selection
- disruptive selection
- stabilizing selection
Directional selection
When conditions favour individuals exhibiting one extreme of a phenotypic range
how does directional selection shift a population’s frequency curve for the phenotypic character
in one direction or the other
when is directional selection common
when population’s environment changes or when members migrate to new habitat
what type of selection is this
directional selection
what type of selection is this
disruptive selection
what type of selection is this
stabilizing selection
disruptive selection
When conditions favour individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
stabilizing selection
Acts against BOTH extreme phenotypes and favours intermediate variants
what is the outcome of a stabilizing selection
Reduces variation and tends to maintain the status quo for a phenotypic character
what happens when there is an increase of favourable traits
match between species and environment improves = adaptive evolution occurs
adaptive evolution is an _______ process
continuous, dynamic
true or false
genetic drift and gene flow can consistently increase allele frequency for better survival
FALSE
ONLY evolutionary mechanism that consistently leads to adaptive evolution
natural selection
sexual selection
Form of selection where individuals with certain inherited traits are more likely than others to obtain mates
sexual selection can result in
sexual dimorphism
two types of sexual selection operations
intrasexual selection
intersexual selection
intrasexual selection
selection within the same sex = individuals of the same sex compete directly for mates of the opposite sex
intersexual selection is also called
mate choice
intersexual selection
Individuals of one sex (females usually) are choosy in selecting their mates from the other sex
How do female preferences for certain male traits evolve in the first place
Females prefer male traits that are correlated with “good genes”
Frequency-dependent selection
The fitness of a phenotype depends on how common it is in the population
the frequency-dependent selection would favour the phenotype that is
least common
how is evolution limited by historical constraints
Evolution doesn’t scrap the ancestral form and build a new structure from scratch - co ops existing structures and adapts them to new situations
heterozygous advantage is a form of _____ selection
stabilizing
what was the next great advance in evolutionary biology
genetics
particulate inheritance
trait inherited in chunks called genes
phenotype is made up of BOTH
genetics and environment
if there is zero heterozygosity there then
is no genetic variation
plasticity
a phenotype that changes because of environmental pressures (like predation)
is plasticity heritable
NO
what is more important in genetic variation mutations or sexual reproduction
sexual reproduction
HW is the _____ hypothesis
null
if a population is AT HW then it’s
NOT evolving
if a population that’s evolving at HW equilibrium
NO
genetic variation AMONG a population is _____ based on drift
increasing
genetic variation WITHIN a population is _____ based on drift
decreasing
when does heterozygote advantage reflect directional selection
when it shows the extreme phenotype (biggest of anything)
when does heterozygote advantage reflect stabilizing selection
when it shows the intermediate phenotype
what specifies advantageous and disadvantageous traits
the environment
how does natural selection show chance
the environment individuals are found in/the variation that exists in a pop
how does natural selection show sorting
sorting which phenotype/genotype is selected
what level is evolution measured at
population
what level does NS act on
individuals NOT on genotype
does the mean phenotype change in directional selection
YEs
does the mean phenotype change in disruptive selection
NO
genetic drift ________ genetic variation WITHIN a population
decreases
genetic drift ________ genetic variation AMONG a population
increases
gene flow ________ genetic variation WITHIN a population
increases
gene flow ________ genetic variation AMONG a population
decreases
does natural selection decrease fitness
NO
