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11.1 Genetic Variation Within Population KEY CONCEPT A population shares a common gene pool. 11.1 Genetic Variation Within Population Genetic variation in a population increases the chance that some individuals will survive. • Genetic variation leads to phenotypic variation. • Phenotype – a collection of all an organism’s physical characteristics. Ex: height, skin color, hair color etc… • Phenotypic variation is necessary for natural selection. • Genetic variation is stored in a population’s gene pool. – made up of all alleles in a population – Allele – any of the alternative forms of a gene that occurs at a specific place on a chromosome. • allele combinations form when organisms have offspring (organisms get one allele from each parent). • Simplified example: Frogs have a gene for skin color (green or brown). G represents green and g represents brown. G is dominant and g is recessive. 11.1 Genetic Variation Within Population • Allele frequencies measure genetic variation. Allele frequency is the ratio of one allele to the total number of the alleles for that gene in the gene pool. – measures how common allele is in population – can be calculated for each allele in gene pool Predict: If brown skin color became advantageous, what would likely happen to the frequencies of alleles G and g in this gene pool? 11.1 Genetic Variation Within Population Genetic variation comes from several sources. • 1. Mutation is a random change in the DNA of a gene. – can form new allele – can be passed on to offspring if in reproductive cells • 2. Recombination forms new combinations of alleles. – usually occurs during meiosis – parents’ alleles arranged in new ways in gametes –egg/sperm cells 11.1 Genetic Variation Within Population Genetic variation comes from several sources. • Hybridization is the crossing of two different species. – occurs when individuals can’t find mate of own species – topic of current scientific research as a possible 3rd source of genetic variation 11.1 Genetic Variation Within Population Analyze and Infer • A. What is the relationship between allele frequencies and a gene pool? • B. Why aren’t mutations in nonreproductive cells sources of genetic variation?