What is allele frequency? 17.1 Genes and Variation LT: Analyze shifts (changes) in numerical distribution of traits and use these shirts as evidence to support evolution by natural selection Focus Questions: What is allele frequency? What causes allele frequency to change in a population?

FQ: How does evolution by natural selection change a population over time? ET: Get into a group of 3 and pick up one copy of the lab from the front of the room Read the lab with your group of 3

Gene Pool: The combined genetic information of all the members of a particular population All the members of a population may interbreed so they share a group of common genes

What are the 2 main sources of genetic variation? Mutations: Any change in a sequence of DNA Q: how do mutations occur? radiation, environment, replication of DNA Gene Shuffling: Your 23 pairs of chromosomes can produce 8.4 million different combinations of genes! Q: how do chromosomes get arranged so differently? Independent assortment and crossover

Directional Selection When nature selects individuals at one end of the bell curve as the fittest

Stabilizing Selection When nature selects individuals in the middle of the curve as more fit and the bell narrows

Disruptive Selection When nature selects individuals at opposites ends of the curve as more fit.