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How Do Genes Make Evolution Possible? Essential Understanding • The diversity of life is a result of ongoing evolutionary change. Species alive today have evolved from ancient common ancestors Genotype vs Phenotype • Typical plants and animals contain 2 sets of genes, one from each parent • Specific forms of a gene, alleles, vary between individuals • Genotype is a particular combination of alleles whereas phenotype is the physical expression of the genotype Natural selection • Natural selection acts on phenotype, not genotype • If an organism has a phenotype that is adaptive, it may survive and pass the genes that code for that trait to its offspring Populations and gene pools • A population is a group of individuals of the same species in the same area • A gene pool consists of all the genes that are present in a population • Allele frequency is the number of times an allele appears in a gene pool Allele Frequency How many mice are of each genotype? BB – Bb – bb – Evolution of populations • Evolution involves a change in the frequency of alleles in a population over time Sources of Genetic Variation • Mutations – Changes or mistakes in the genetic code • Genetic recombination – During sexual reproduction, genes are often moved and swapped • Lateral gene transfer – Passing of genes between individuals instead of through offspring (Bacteria) Single gene vs Polygenic Traits • Single gene traits – Traits that are controlled by a single gene – Presence or absence of something • Polygenic traits – Traits that are controlled by more than one gene – Traits where there are various levels