Allele frequencies can change creating
microevolution
•Individuals
of
one genotype reproduce more often with each other
•Individuals
migrate between populations
•Population
size
is small or a group becomes reproductively isolated within a larger
population
•Mutation
introduces new alleles or new copies of alleles
•Individuals
with a particular genotype are more likely to have viable, fertile
offspring
Hardy-Weinberg Equilibrium
A condition in which allele frequencies remain
constant
is called Hardy-Weinberg equilibrium
Application of Hardy-Weinberg Equilibrium:
calculating risk
Carrier Frequency for Cystic Fibrosis
Application of Hardy-Weinberg Equilibrium:
DNA identification
Application of Hardy-Weinberg Equilibrium:
DNA identification
•the
DNA pattern observed
from the population is calculated using the
frequency of alleles in that population.
•Genotype
frequencies of
unlinked loci are multiplied.
•Allele
frequencies vary in
different populations. Use of correct
population information is important.
Allele frequencies can change creating
microevolution
•Individuals
of
one genotype reproduce more often with each other
•Individuals
migrate between populations
•Population
size
is small or a group becomes reproductively isolated within a larger
population
•Mutation
introduces new alleles or new copies of alleles
•Individuals
with a particular genotype are more likely to have viable, fertile
offspring
Nonrandom mating
Random
mating
occurs when individuals of one genotype mate randomly with individuals
of all
other genotypes.
Nonrandom
mating indicates individuals of one genotype reproduce more often with
each
other
•Ethnic
or religious
preferences
•Isolate
communities
–Worldwide,
1/3
of all marriages are between people born within 10 miles of each other
•Cultures
in
which consanguinity is more prominent
–Consanguinity
is marriage between relatives
e.g.
second or
third cousins
Migration
When people
move, their genes go with them.
The genetic
effects of migration are reflected in current populations.
Allele
frequencies change when alleles are disproportionately distributed in
the migrants.
Migration
•Changes
in allele frequency
can be mapped across geographical or linguistic regions.
•Allele
frequency
differences between current populations can be correlated to certain
historical
events.
Mapping a trait geographically can suggest
patterns of
migration
Frequencies of galactokinase deficiency
decrease westward
from home of the Viax Roma in
Gradients in allele frequencies between
successive
neighboring populations are called clines.
Genetic Drift
Changes
in
allele frequency occur when gametes do not reflect the allele
frequencies in
parents by random chance.
This random sampling error is called genetic
drift.
Genetic drift is more pronounced in small
populations.
Genetic Drift
Events that
create small populations enhance the effect of genetic drift.
Founding a new population
Bottlenecks (natural disaster, famine)
Geographic separation (islands)
Linguistic differences
Genetic Drift
Founder
effects
refer to the genetic impact of starting a new population from a
relatively
small group of people.
Mutation can introduce new alleles.
Mutation can convert one allele to another.
Mutation has a minor impact unless coupled with
another
effect (small population size, selection).
Mutation
Allele frequencies change in response to
mutation.
Natural Selection
The differential survival and reproduction of
individuals
with a particular phenotype is called natural selection.