Allele frequency may change in
populations due to:
mutation - rare, slow to alter allele
frequency
error in replication
environmental cause
migration - infusion of contrasting
genes from new individuals of a species.
genetic drift - genetic recombination
during
sexual reproduction may allow
some alleles to
be lost in a random
fashion. Especially true in small
populations.
Non-random mating - result of a
population reproducing sexually with
closely related members. This may
result from a decreased mating
population from either natural or artificial
means which prohibit random mating.
Results are more homozygous alleles
and inbreeding.
Selection - alleles removed from
breeding population or increased in
abundance in a breeding population.
artificial - human guidance of
breeding results
in artificial
development of traits.
natural - alleles for negative traits are
selected
against due to mortality of
carriers. Alleles for
positive traits
are selected for by passage of
genome to future generations.
Hardy-Weinberg Principal of genetic
equilibrium
Assumptions:
1) no mutations occur
2) no individuals enter or leave
through
migration
3) The population is large
4) individuals mate randomly
5) natural selection does not occur
If any of the assumptions are not met,
then evolution will occur.
Most alterations in the genome have
no significant phenotypic effect.
Statistically speaking, many such
alterations must occur before a
phenotypic change occurs.
When an observable trait does occur
in offspring, the change is usually
negative.
Positive changes are extremely rare.
Changes which have no observable
effect at one point in time may have
dramatic effect in the future when the
environment changes.
Speciation - local populations become
highly specialized through
microevolution. Continued speciation
through time results in a
macroevolutionary change, the
development of a new species.
Isolation of a population
Geographic
Island
Darwin’s finches
Mammoths
Desert pupfish
Behavioral
Bird stratification
5-lined & broadhead skinks
Prince William sound orca
Sexual selection
Ecological
steep slopes
windward & leeward
Temporal
fungi
tucahei (New Zealand)
Mechanical
Bacculum
Rate of speciation
Gradualism
Punctuated equilibrium
Adaptive radiation
filling of unoccupied niches of new
habitat
Darwin’s finches
Convergent evolution vs. divergent
evolution
unrelated species
same
species
Coevolution - under our noses
Trees & microrhizal fungi
Iris & wasp
Bats & cacti or bats & tropical fruit
trees
Extinction