Download Genetic Variation and Equilibrium

Genetic Variability and
Equilibrium
What you have already learned…
1. Genetic variation exists within inherited traits in
every population.
2. Variation exists in the phenotypes of individuals
within populations.
3. Genetic variation can either help or harm
individuals.
4. It is better to have variation within a population.
– Environmental change occurs and wipes out half of
population that did not have the traits to survive; other
phenotypes that existed in the population did survive
and can continue to breed successively.
Genetic Variation
• Populations with lots of genetic
variation normally also have a lot of
variation in phenotype
• Variation is good in a population
because it allows the species to adapt
to a changing environment
Gene Pool
• The genetic variation of a population is
stored in a populations gene pool
• The gene pool is the set of all the
different alleles within a population
• Different combinations of alleles occur
when individuals in the population
mate
Factors that Influence Genetic
Variability
1. Gene Flow: the
movement of genes
from one population
to another as
individuals move
between populations
– Increases the
genetic variation of
the receiving
population
Gene Flow (cont.)
• The less gene flow there is between
populations the more genetically
different the two populations become
as they each adapt to their different
environments
– Eventually the two populations may
become so different that they form
different species
Factors that Influence Genetic
Variability
2. Genetic drift:
changes in allele
numbers due to chance
–
–
Causes a loss in
genetic diversity
Change of alleles is
more noticeable in
smaller populations.
Bottleneck Effect
• Occurs when some kind of event
greatly reduces the size of a
population
Founder Effect
• Occurs when a small number of
individuals colonize a new area
Factors that Influence Genetic
Variability
3. Sexual Selection (nonrandom mating):
occurs when certain
traits increase mating
success
–
–
–
Males compete for
females
Males display traits that
attract females
The alleles for these
traits become more
common because the
individuals with the traits
mate more successfully
Factors that Influence Genetic
Variability
4. Mutations:
increase the
genetic variation
by introducing
new alleles
5. Natural Selection:
allows for the most
favorable phenotypes
to survive and be
passed on to future
generations.
Hardy Weinberg Equilibrium
• The frequency of alleles can remain
constant if certain conditions are met.
• When a population’s allele frequency
remain the same that population is
said to be in Hardy-Weinberg
Equilibrium (genetic equilibrium)
Genetic Equilibrium (HardyWeinberg Principle)
• Five conditions that are required to
maintain genetic equilibrium:
1. The population must be very large, no
genetic drift occurs.
2. No migration into or out of a population
3. There must be random mating
4. There must be no mutations within the
gene pool.
5. There must be no natural selection.