Transcript Evolution #2 - Mr. Eeds Biology

NOTES: Evolution of
Populations
Why is genetic variation important?
variation
global
warming
survival
EXTINCTION!!
no variation
Why is genetic variation important?
variation
no variation
Why is genetic variation important?
divergence
variation
no variation
NO DIVERGENCE!!
GENETICS & EVOLUTION
• Gene pool
– consists
of all the
genes that
are present
in a
population
• Relative frequency – the number of
times that an allele occurs in a
gene pool
–Ex. In a mouse population, the
dominant allele for black fur may
appear 40% and the recessive
allele for brown fur may appear
60%
• In genetic terms, evolution is any
change in the relative frequency of
alleles in a population
• When individuals at one end of the curve
have higher fitness than individuals in the
middle or at the other end, Directional
Selection takes place.
• The range of phenotype shifts.
• When individuals
near the center of
the curve have
higher fitness than
individuals at
either end of the
curve, stabilizing
selection takes
place.
• Stays at center.
• When individuals at the upper and
lower ends of the curve have higher
fitness than individuals near the middle,
disruptive selection takes place.
Three Forms of Natural Selection
• Natural selection is not the only source of
evolutionary change
• In small populations, an allele can become
more or less common simply by chance.
• This kind of random change is called
genetic drift.
• In small populations, individuals that carry
a particular allele may leave more
descendants than other individuals, just by
chance.
• Over time, a series of chance occurrences
of this type can cause an allele to become
common in a population.
Genetic Drift
• Populations not individuals evolve.
• A population in which the frequency
of alleles remains the same over
generations as being in genetic
equilibrium.
GENETIC VARIATION
• 2 Main Sources of Genetic
Variation:
• 1. Mutations – change in a
sequence of DNA
• 2. Gene shuffling that results
from sexual reproduction
DEFINITIONS
• Species – interbreeding
populations of organisms that can
produce fertile offspring
• Speciation – formation of a new
species
• Reproductive Isolation – when
members of two populations
cannot interbreed and produce
fertile offspring
How do organisms become isolated?
Types of Reproductive Isolation
• 1. Behavioral isolation – when
2 populations are capable of
interbreeding but have
differences in courtship rituals
or other reproductive
strategies that involve
behavior
• 2. Geographic
isolation – when 2
populations are
separated by
geographic
barriers such as
rivers, mountains
or bodies of
water, highways
• Temporal Isolation: Occurs
when populations are capable
of interbreeding, but each
breed at different times.
Morning
Blooms at
different
times of
day.
Night
Noon
Speciation in Darwin’s
Finches
• Darwin found over a dozen different
species of finches on the Galapagos
Islands that all evolved from a common
ancestor
• How?
• A few finches (original species) flew
or were blown to one of the Galapagos
Islands
• Then some birds migrated to
neighboring islands and because the
environments were different they
adapted to their own environments
and became separate species
 Speciation in the Galapagos
finches occurred by:
• founding of a new population
• geographic isolation
• changes in the new
population’s gene pool
• reproductive isolation
• ecological competition
DARWIN’S FINCHES
• Darwin’s Finches are an
example of adaptive radiation
• Adaptive radiation is when a
single species has evolved into
diverse forms that live in
different ways