Everybody in the “gene pool” 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.