Population_evolution

Population_evolution - Biology 111, Principles of Biology...

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Biology 111, Principles of Biology Lecture Outlines Evolution of Populations A primary consequence of natural selection is that allele frequencies in a population will change over time (MICROEVOLUTION). NOTE: Natural selection acts upon individuals, but it is the POPULATION as a whole that evolves (individuals do not evolve). Changes in allele frequencies affect populations, not individuals. "A POPULATION is a localized group of individuals that are capable of interbreeding and producing fertile offspring" (Campbell) Populations may be isolated (as in Darwin's finches on the Galapagos Islands), or they may overlap to some extent (see Figure 23.3): The GENE POOL of a population is the sum of all alleles at all loci in all individuals. Microevolution therefore describes changes in the gene pool of a population over time. In the early 1900's Hardy & Weinberg independently derived a mathematical way to describe gene pools that are not undergoing evolution The Hardy & Weinberg theorem basically states that as long as only Allele frequencies in a population do not change over time Genotype frequencies in a population do not change over time This phenomenon is known as HARDY-WEINBERG EQUILIBRIUM The H-W theorem relies on a few assumptions: population must be large mating must be random If true, then a population may be treated as just a collection of alleles that combine randomly to produce the next generation The genotype & phenotype frequencies in the next generation will be determined by allele frequencies in the population (see Figure 23.4): Consider a Hardy & Weinberg population of in which flower color is determined by two incompletely dominant alleles at a single gene:
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If the parental generation includes 320 RED (C R C R ), 160 PINK (C R C W ), and 20 WHITE (C W C W ) individuals, predict the genotype & phenotype ratios expected in the F1 generation (see Figure 23.5): Hardy & Weinberg recognized that the normal process of sexual reproduction (including independent assortment, recombination, and random fertilization) does not result in microevolution (changes in allele frequencies in a population over time) Mathematical statement of H-W Equilibrium: If f(A) = p and f(a) = q, then f(AA) = p 2 f(Aa) = 2pq f(aa) = q 2 We can also use the H-W equation to determine whether a population is genetically stable, or whether microevolution is occurring. For example, determine whether the following population is in H-W equilibrium: Flower colors in the population are: 280 RED (C R C R ), 40 PINK (C R C W ), and 80 WHITE (C W C W ) We can also use the H-W equation to determine whether a population is genetically stable, or whether microevolution is occurring.
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This note was uploaded on 04/17/2008 for the course BIOL 111 taught by Professor Lux during the Fall '07 term at Lander.

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Population_evolution - Biology 111, Principles of Biology...

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