Transcript Concept 14.4: Microevolution is a change in a population’s

Microevolution
Everybody in the “gene pool”
Microevolution
• A generation to generation change in
frequency of alleles within a population.
• Alleles = alternate forms of a gene
• If gene frequencies are not changing in a
population, we say that this population is
at Hardy-Weinberg equilibrium.
Hardy-Weinberg Equilibrium
• Formula: p2 + 2pq + q2 = 1
• p2 = f(AA), q2 = f(aa), 2pq = f(Aa)
• Based on assumptions:
– Large population
– Random mating
– No natural selection
– No mutation
– No migration
• No population is ever at equilibrium!
Examples of Microevolution
House sparrows adapting to climate in North America
Insects evolving resistance to pesticides
Gene Pool
• All of the alleles in all of the individuals
that make up a population.
• The gene pool is where genetic
variation is stored (next generation
draws from pool).
• Genetic variation is the “raw material”
of evolution.
• Population= the smallest level for
evolution to occur (not individual)
• Microevolution reflects gene frequency
changes in a population’s gene pool.
2 processes increase genetic variation
1. Mutation: a change in an organism’s DNA
– If this mutation is carried by a gamete, the
mutation enters the population’s gene pool.
– Adds variation in a random manner.
2 processes increase genetic variation
2. Genetic Recombination: the result of the
processes of meiosis and fertilization
– Alleles in the gene pool are “shuffled” and
“dealt” to the offspring in a random manner.
3 processes change the gene pool
1. Genetic Drift: change in the gene pool
due to chance events
– The smaller a population, the more impact
genetic drift can have.
3 processes change the gene pool
2. Gene flow: change in the gene pool due
to the exchange of genes with another
population
3 processes change the gene pool
3. Natural Selection: change in the gene
pool due to differences in survival and
reproductive success among members of
the varying population
•Certain alleles
become more
common.
•This leads to
adaptations.
Biological Fitness
• The contribution that an individual makes
to the gene pool by producing offspring.
• It is NOT usually direct contests between
individuals.
Finch Fitness
• The Grants studied
the medium ground
finch for 30 years.
• Discovered
selective pressures
for beak size
affected finch
fitness.