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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.