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CHAPTER 16 NOTES GENETICS & EVOLUTION Gene pool – consists of all the genes that are present in a population Relative frequency – the number of times that an allele occurs in a gene pool – Ex. In a mouse population, the dominant allele for black fur may appear 40% and the recessive allele for brown fur may appear 60% In genetic terms, evolution is any change in the relative frequency of alleles in a population GENETIC VARIATION 2 Main Sources of Genetic Variation: 1. Mutations – change in a sequence of DNA 2. Gene shuffling that results from sexual reproduction DEFINITIONS Species – interbreeding populations of organisms that can produce fertile offspring Speciation – formation of a new species Reproductive Isolation – when members of two populations cannot interbreed and produce fertile offspring How do organisms become isolated? 1. Behavioral isolation – when 2 populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior 2. Geographic isolation – when 2 populations are separated by geographic barriers such as rivers, mountains or bodies of water Speciation in Darwin’s Finches Darwin found over a dozen different species of finches on the Galapagos Islands that all evolved from a common ancestor How? A few finches (original species) flew or were blown to one of the Galapagos Islands Then some birds migrated to neighboring islands and because the environments were different they adapted to their own environments and became separate species DARWIN’S FINCHES Darwin’s Finches are an example of adaptive radiation Adaptive radiation is when a single species has evolved into diverse forms that live in different ways