Download Evolution as Genetic Change

Evolution as Genetic Change
Subtitle
Control of Natural Selection
• Natural Selection can affect the
distributions of phenotypes in any of three
ways:
• Directional selection
• Stabilizing selection
• Disruptive selection
Directional Selection
• Evolution favors the
most fit species.
• Causes an increase in
the number of
individuals with favored
trait to one end of a
curve.
Stabilizing Selection
• When individuals
with the desirable
traits are towards the
center of the curve.
• Major Point: The
extremes don’t
survive.
Disruptive Selection
• When the individuals
at the extremes have
the highest fitness.
Genetic Drift
• In a smaller population,
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.
• This can be caused by the
bottle neck effect.
Speciation
• Four things that lead to speciation:
• Reproductive isolation
• Behavioral isolation
• Geographic isolation
• Temporal isolation
Reproductive Isolation
•When members of two populations
cannot interbreed and produce
fertile offspring.
Behavioral Isolation
• When two populations are capable of
interbreeding but have differences in courtship
rituals or other reproductive strategies that
involve behavior.
• Ex. Eastern Meadowlark/Western
Meadowlark
• Their songs are different and so don’t
reproduce.
Geographic Isolation
• Two populations are separated by
geographic barriers.
• Ex. Rivers, mountains, etc.
Temporal Isolation
•When two or more species
reproduce at different times.