Download 16.2 Evolution as genetic change rev 11

16.2
Evolution as Genetic Change
The effects of Natural Selection cause changes
in whole populations, not just in individuals
.
Therefore the genetics of the population will change
.
Evolution of dolphins
Natural Selection on Polygenic Traits

Natural selection operates on variations of traits
within a population.

The distribution of traits in a population changes
over time.

There are 3 general patterns of trait changes in a
population as a result of natural selection.
1. DIRECTIONAL SELECTION:
An extreme
phenotype
becomes a
favorable
adaptation
2. STABILIZING SELECTION:
The average
phenotype is
favored for
survival.
The extreme
phenotypes are
un-favored.
3. DISRUPTIVE SELECTION
The average
phenotype is not
favorable, but the
extreme phenotypes
become favored
adaptations.
Can eventually lead
to 2 species.
Hardy-Weinberg Principle

If the allele
frequencies do not
change, the
population will not
evolve.

This will be true if 5
conditions are met.
Flamingo population
Hardy-Weinberg Genetic
Equilibrium





Random mating. [Seldom happens.]
Very large populations. [Can happen.]
No immigration and no emigration. [Can
happen.]
No mutations. [Seldom happens.]
No natural selection. [Seldom happens.]
Therefore, evolution is a given, it cannot
be stopped. There are no conditions
known under which evolution does not
happen!
Evolution of land animals
Genetic Drift

Happens in small
populations.

An allele becomes
more or less
common easier.

Random chance
events lead to
these changes in
gene frequencies.
Bull Tule Elk at Pt. Reyes
Founder Effect
Founding populations are completely separated from the
original population, as well as from other founding
populations when they colonize a new habitat.