KEY CONCEPT A population shares a common gene pool.

Genetic variation leads to phenotypic variation. 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.

Allele frequencies measure genetic variation 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?

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

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

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?