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Evolution of A new Species Genetic Variation Sources of Genetic Variety • The two main sources of genetic variation in a population are mutations and sexual reproduction • Sexual reproduction shuffles parent genes/DNA through meiosis • Mutations create constant random variety that sometimes makes an organism more fit for its environment. EX: A mutation that gave brown bears white fur in the polar regions making white polar bears more fit for survival. “What Molecules Do” Video Mutations=Variety Lethal Alleles • How are lethal alleles maintained in a population? Shouldn’t natural selection remove these? • Alleles that are lethal in a homozygous individual may be carried in a heterozygous individual. • For example: If two parents are carriers of a bad allele and an individual inherits both bad alleles they will get the lethal disease. Gene Pool• consists of all genes, including all the different alleles, that are present in a population. Allele Frequency • number of times an allele occurs in a gene pool – EX: How many in this class have at least one dominant allele for brown eyes • Sexual reproduction produces different phenotypes, but it does not change the relative frequency of alleles in a population. Gene Pool for Fur Color in Mice How is evolution defined in genetic terms? – In genetic terms, evolution is any change in the relative frequency of alleles in a population. What is Speciation • Speciation is the formation of a new species • Speciation is caused by reproductive isolation – Reproductive Isolation is when two members of a population cannot mate. There are 3 types of reproductive isolation. Reproductive Isolation • #1. Behavioral Isolation is when genetically similar populations are able to breed but don’t due to differing mating rituals. – http://www.youtube.com/watch?v=oYmzdvMoUU A&feature=related – http://www.youtube.com/watch?v=MPWOZZIzDy o&feature=related Reproductive Isolation • #2. Geographic Isolation is when two members of a population are separated by barriers such as mountains, canyons, bodies of water, etc. • EX: Squirrels on opposite sides of the Grand Canyon Reproductive Isolation • #3. Temporal Isolation is when members of a population mate at different times of the year. • EX: Different frogs mate in different months Equilibrium • Theoretical model of a population • 5 Conditions: 1) No net mutations 2) NO immigration/Emigration 3) VERY large population 4) Individuals mate randomly 5)Selection doesn’t occur The Equation Hardy-Weinberg equilibrium=predict population genotypes p=dominant allele (A) q= recessive allele (a) The sum of p+q=1,then solve p2 + 2pq + q2 = 1 p=dominant allele (A) q= recessive allele (a) The sum of p+q=1,then solve p2 + 2pq + q2 = 1 Use the equation to solve this problem What is p if q = 30% p + .30 =1 p=.70 In this population what percent of individuals are homozygous dominant (AA)? p2= .72=.49=49% In this population what percent of individuals are heterozygous (Aa)? 2pq= 2(.7)(.3)= .42= 42% Use the equation to solve this problem What is p if q = 30% p + .30 =1 p=.70 In this population what percent of individuals are homozygous dominant (AA)? p2= .72=.49=49% In this population what percent of individuals are heterozygous (Aa)? 2pq= 2(.7)(.3)= .42= 42% -PRACTICE Disrupting Equilibrium • 1) Mutations- a change in DNA changes allele frequencies • 2) Gene flow- genes move in and out of the population due to immigration and emigration • 3) Genetic drift is a change in allele frequencies • Genetic drift operates most strongly in small populations • 4) Non random mating- whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual’s success at mating • 5) 3 types of selection Genetic Drift • A random change in allele frequency (can be caused by fire, flood, etc) – In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Genetic Drift •Genetic Drift Genetic drift • Active art • www.PHSchool.com • Code cbp-5162 •Descendants Genetic Drift Population A Population B Founder effect • Founder effect • When allele frequencies change as the result of the migration of a small subgroup of a population. • How does genetic drift differ from natural selection in the way it changes the genetic makeup/allele frequency of a species over time? Stabilizing Selection Favors the formation of average/intermediate traits. Disruptive Selection Favors extreme traits rather than average traits Directional Selection Favors the formation of a more-extreme trait. Does Natural Selection act on the phenotype or genotype of a species? • Phenotype – predators can only see the outside physical appearance of an individual making them less fit or suited for their environment.