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Genetics and Evolution Genetics and Evolution • Populations evolve, NOT individuals! • Evolution = changes in a population’s genes over time Vocabulary • Gene pool = a collection of all of the possible genes in a population • Allelic frequency = the % of an allele in a gene pool • Genetic equilibrium = occurs when allele frequency does not change (NO EVOLUTION!) Genetic equilibrium • So what are some ways that the genetic equilibrium changes? 1. mutation – most mutations are lethal and those organisms do not survive – occasionally a mutation results in a useful variation and the new gene is selected for Genetic equilibrium • So what are some ways that the genetic equilibrium changes? 2. genetic drift – chance events alter the gene pool – usually affects smaller populations – Ex. Amish population of 12,000 carries a recessive allele that results in short arms and legs and extra fingers and toes Genetic equilibrium • So what are some ways that the genetic equilibrium changes? 3. migration - transport of genes to and from a population Genetic equilibrium • So what are some ways that the genetic equilibrium changes? 4. natural selection – most significant effect on genetic equilibrium Natural Selection can Change the Genetic Equilibrium in 3 Ways Changes in genetic equilibrium 1. Stabilizing Selection: – favors the average form of a trait – results in less variation in a population – Ex: average sized spiders Changes in genetic equilibrium 2. Directional Selection – favors one extreme form of a trait – results in species showing one extreme form of a trait – Ex: woodpeckers with long beaks Changes in genetic equilibrium 3. Disruptive Selection – favors both extreme forms of a trait – can result in 2 new species over a long period of time – Ex: light and dark limpets Evolution of a new species • Speciation = the evolution of a new species (when interbreeding is prevented) What leads to speciation? 1. Geographic isolation EX: Tree frog population with a river separating them What leads to speciation? 2. Reproductive isolation – EX: Genetic- genetic material becomes so different that fertilization can’t occur – EX: Behavioral- one pop of frogs mates in the fall, the other in the spring What leads to speciation? 3. Change in chromosome number (polyploidy) – EX: nondisjunction occurs during meiosis leaving the zygote (4n) instead of 2n; wheat, cotton, and apples are examples – Only takes one generation to create a new species Speciation rates 1. Gradualism: a new species forms through a gradual change of adaptations 2. Punctuated equilibrium a new species forms quickly in bursts, with long periods of genetic equilibrium in between; 10,000 years or less Patterns of evolution 1. Adaptive radiation: an ancestral species evolves into a wide variety of species to occupy their own niche or diverse habitat EX: honeycreepers on the Hawaiian Islands EX: Darwin’s finches on the Galapagos Islands Patterns of evolution 2. Divergent Evolution: species that were similar become different in order to adapt to different environments (Adaptive radiation is a type of divergent evolution) Patterns of evolution 3. Convergent Evolution : species that were unrelated evolve similar traits in order to occupy similar environments in different parts of the world EX: pipe cactus and Euphorbia – both have fleshy body type and no leaves to survive the desert but totally unrelated