Evolution of Populations
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Transcript Evolution of Populations
Ch. 16 Evolution
of Populations
Variations and Gene Pools
pool – consists of all genes,
including all the different alleles, that are
present in a population.
Gene
frequency – the number of times
that the allele occurs in a gene pool,
compared with the number of times other
alleles for the same gene occur.
Relative
Variations and Gene Pools
Sources of Genetic Variation
The
2 main sources of genetic variation
are mutations & the genetic shuffling
that results from sexual reproduction.
Single-Gene & Polygenic
Traits
The
# of phenotypes produced for a given
trait depend on how many genes control
the trait.
Single-gene trait - controlled by a single
gene, that
has 2 alleles
Ex.) Widow’s Peak
Single-Gene & Polygenic
Traits
Polygenic
traits - trait controlled by 2 or
more genes
Ex.) Height in humans
Evolution as Genetic Change
Evolutionary fitness can be viewed as an
organism’s success in passing genes to the next
generation.
Evolutionary adaptation can be viewed as any
genetically controlled trait that increases an
individual’s ability to pass along its genes.
Evolution as Genetic Change
NS
never acts directly on genes.
NS can only affect which individuals
survive & reproduce, & which do not.
Also, remember that it is populations, not
individual organisms, that can evolve over
time.
NS on Single-Gene Traits
NS
on single-gene traits can lead to
changes in allele frequencies & thus to
evolution.
NS on Polygenic Traits
NS
can affect the distributions of
phenotypes in any of 3 ways:
-directional selection
-stabilizing selection
-disruptive selection
NS on Polygenic Traits
Directional
Selection - occurs when
individuals at 1 end of the curve have
higher fitness than individuals in the
middle or at the other end.
NS on Polygenic Traits
Stabilizing
selection - occurs when
individuals near
the center of a curve
have higher fitness
than individuals at
either end.
NS on Polygenic Traits
Disruptive
selection - when individuals at
the upper & lower ends of the curve have
higher fitness than individuals near the
middle.
Genetic Drift
drift – random change in allele
frequencies that occurs in small
populations.
Founder effect - situation in which allele
frequencies change as a result of the
migration of a small subgroup of a
population.
Genetic
Genetic Drift
Evolution vs. Genetic
Equilibrium
Hardy-Weinberg
Principle-allele
frequencies in a population will remain
constant unless one or more factors cause
those frequencies to change.
Genetic equilibrium - when allele
frequencies remain constant, the
population will not evolve.
Evolution vs. Genetic
Equilibrium
5
conditions are required to maintain genetic
equilibrium:
-random mating
-large population
-no movement into/out of pop.
-no mutations
-no NS
Overuse of Antibiotics
People
may be overusing antibiotics.
Doctors may prescribe them for diseases
which they are not effective.
This wide use of antibiotics has caused
many bacteria to evolve resistance to
antibiotics.
The Process of Speciation
Speciation
- formation of a new species
The gene pools of 2 populations must
become separated for them to become
new species.
Isolating Mechanisms
As
new species evolve, populations
become reproductively isolated from each
other.
Reproductive isolation - when members
of 2 populations can’t interbreed &
produce fertile offspring
Isolating Mechanisms
Behavioral
isolation - when 2
populations are capable of interbreeding
but have differences in courtship rituals or
other reproductive strategies that involve
behavior
Ex.) Birds with
mating songs
different
Isolating Mechanisms
Geographic
isolation - 2 populations are
separated by geographic barriers like
rivers, mountains, or bodies of water
Ex.) Squirrels split by Colorado River
Isolating Mechanisms
Temporal
isolation - when 2 or more
species reproduce at different times
Ex.) Orchids releasing pollen on
different days
Testing NS
in
Nature
Speciation in
Darwin’s Finches
Speciation
in the Galapagos
finches occurred by:
founding a new population
geographic isolation
changes in the new population’s gene
pool
reproductive isolation
ecological competition
Patterns of Evolution
Macroevolution - large-scale evolutionary
patterns & processes that occur over long
periods of time
6 important topics in macroevolution are:
•
•
•
•
•
•
extinction
adaptive radiation
convergent evolution
coevolution,
punctuated equilibrium,
changes in developmental genes
Patterns of Evolution
Extinction:
More than 99% of all species are now extinct
It usually happens for a reason; species
compete for resources, & environments
change
Some species adapt &
survive, others become
extinct
Patterns of Evolution
Adaptive
radiation - when a single species
has evolved, through NS, into diverse
forms that live in different ways
Ex.) Darwin’s Finches
Patterns of Evolution
Convergent
evolution - when unrelated
organisms begin to resemble one another
It has occurred in both plants
animals
Ex.) Swimming animals
&
Patterns of Evolution
Coevolution
- when 2 species evolve in
response to changes in each other over
time
Ex.) Orchid has long spur with nectar in its tip,
a Hawk moth has equally long feeding tube
that allows it to feed on the nectar
Patterns of Evolution
Punctuated
equilibrium - a pattern of long,
stable periods interrupted by brief periods
of more rapid change