Download 11.3 Other Mechanisms of Evolution TEKS 7D, 7F

11.3 Other Mechanisms of Evolution
KEY CONCEPT
A population shares a common gene pool.
TEKS 7D, 7F
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation in a population is beneficial
because it increases the chance that some
individuals will survive.
• Genetic variation leads to phenotypic
variation.
• Phenotypic variation is necessary for
natural selection.
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation in a population is beneficial because it
increases the chance that some individuals will survive.
• Allele = version of a trait
• Ex: Trait in our population: eye color
Alleles would be brown, blue, green
Ex: Trait for frogs 
skin color
– Alleles: green and
brown
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation in a population is beneficial because it
increases the chance that some individuals will survive.
• Genetic variation is stored in a
population’s gene pool.
–made up of all alleles in a population
–allele combinations form when
organisms have offspring
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
• Genetic variation is measured by allele frequencies.
– measures how common an allele is in a population
– can be calculated for each allele in gene pool
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation comes from several sources.
• Mutation is a random change in the DNA of a gene.
– can form new allele
– can be passed on to
offspring if in
reproductive cells
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation comes from several sources.
• Recombination forms new combinations of
alleles.
– usually occurs
during meiosis
– parents’ alleles
arranged in new
ways in gametes
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic variation comes from several sources.
• Hybridization is the crossing of two
different species.
–occurs when individuals can’t find
mate of own species
–topic of current scientific research
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
KEY CONCEPT
Natural selection is not the only mechanism through
which populations evolve.
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Gene flow is the movement of alleles between
populations.
• Gene flow occurs
when individuals join
new populations and
reproduce.
• (Ex: spores/seeds are
spread to new areas)
bald eagle migration
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Gene flow is the movement of alleles between
populations.
• Lots of gene flow
results in similar
neighboring
populations
bald eagle migration
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Gene flow is the movement of alleles between
populations.
• Limited gene flow
results in an
increased chance
that two populations
will evolve into
different species.
bald eagle migration
11.3 Other Mechanisms of Evolution
Genetic drift is a change
TEKS 7D, 7F
in allele frequencies
due to chance.
• Genetic drift causes a loss of genetic diversity.
• Some alleles increase in frequency,
others may become eliminated from the
population
• It is most common in small populations.
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic drift is a change in allele frequencies due to
chance.
• A population bottleneck can lead to genetic drift.
– It is an event that drastically reduces
population size.
– The bottleneck effect is
genetic drift that occurs
after a bottleneck event.
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
Genetic drift is a change in allele frequencies due to chance.
• A population bottleneck can lead to genetic drift.
• Northern Elephant Seals
– Hunted almost to
extinction
– ~20 survived
– Genetic Variation
drastically reduced
when compared to
Southern Elephant
Seals
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
• The founding of a small population can lead to genetic drift.
– The Founder Effect occurs when a few
individuals start a new population (colonize a
new area).
– The founder effect is genetic drift that occurs
after start of new population.
11.3 Other Mechanisms of Evolution
TEKS 7D, 7F
• Genetic drift has negative effects on a population.
–Population loses genetic variation,
and becomes less likely to have
some individuals that can adapt
–harmful alleles can become more
common due to chance