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Chapter 24 Lecture Outline

Chapter 24 Lecture Outline - Biology 100 Vandan Desai...

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Biology 100 Vandan Desai Chapter 24: Evolutionary Processes (Lecture Outline) -------------------------------------------------------------------------------------------------------------------------- I. Mechanisms of Evolutionary Change A. Evolution is defined as a change in allele frequencies over time i. Cannot occur without genetic diversity ii. Without diversity, there is no variation for natural selection to act on B. glyph817atural selection is the major force that alters the frequencies of alleles i. Natural selection acts on individuals , but evolutionary change occurs in populations —group of individuals from the same species that live in the same area and regularly interbreed ii. Natural selection increases the frequency of alleles that contribute to improved reproductive success iii. Natural selection is the only mechanism that results in adaptation and leads to increased fitness C. Other mechanisms that shift allele frequencies in populations i. Mutation modifies allele frequencies by continually introducing new alleles ii. Gene flow produces allele frequency changes when: 1. New individuals enter an existing population introducing new alleles 2. Individuals leave existing population for elsewhere removing alleles iii. Genetic drift changes allele frequencies randomly II. Mutation A. Mutation occurs constantly i. Mutations can occur during Dglyph817A replication ii. Mutation constantly introduces new alleles into all populations at all loci iii. Mutations increase genetic diversity in populations B. Mutations lead to novel phenotypes by random changes in allele sequences C. Mutation is not an important cause of evolutionary change i. It does not occur often enough ii. Most mutations give rise to deleterious alleles that decrease fitness D. Although mutation rates are low for individual loci (once in 10,000 gametes), they may be high throughout entire genomes E. When combined across entire genomes
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