4How is evolution defined in genetic terms? Evolution is any change in the relative frequency of alleles in the gene pool of a population. (also called microevolution)Period 0 Stopped here 3/18/11Remember: Alleles are different forms of genes.
5Microevolution: The frequency of an allele in a gene pool of a population depends on many factors and can change over time.Over long periods of time, microevolution can lead to macroevolution- change from one species to another.
6What is a GENE POOL?A gene pool is the combined genetic information of all members of a particular population.
10What is relative frequency? The relative frequency of an allele is the number of times that allele occurs in a gene pool compared with the number of times other alleles occur.Expressed in percent.
11Relative Frequency Practice! In a population of 50 students, there are 40 alleles for hitchhiker’s thumb and 60 alleles for a straight thumb. What is the relative frequency of alleles for hitchhiker’s thumb?40/100 = 0.40 = 40%What is the relative frequency of alleles for straight thumb?60/100 = 0.60 = 60%
12How do allele frequencies change during evolution? hill.com/sites/ /student_view0/chapter20/animati on_-_mechanisms_of_evolution.html
13How do allele frequencies change during evolution? Natural Selection which acts on the phenotype rather than the genotype of an organism.Mutations (change in the DNA) which are constantly being generated in a gene pool.Genetic Drift- Random change in allele frequency.Gene Flow- The movement of alleles into or out of the gene pool.Non-random Mating – when females prefer one phenotype over another. Also called sexual selection.
14Remind us: What is Natural Selection? Individuals with favorable genetic variations will survive and reproduce. Individuals that lack adaptations will most likely die before they ever reproduce. Thus, alleles that are favorable will become more common and those that are not will decrease.
15Remind us: What are Mutations? Changes in the DNA and therefore in the genes!
16Genetic Drift is random change in allele frequencies in small populations.
17Genetic Drift is usually caused by natural disasters like a fire or flood. Genetic Drift can cause evolution due to chance rather than natural selection.Period 3 stopped here 2/21/12
18Genetic Drift causes…the founder effect- when a migration of a small subgroup of a population causes a change in allele frequencies. (also called bottleneck affect)Period 5 stopped here 2/21/12
20Genetic Drift often leads to a decrease in variation. Based on this info and what you know about evolution, do you think genetic drift will help a population survive or will it cause the population to go extinct? Why?
21Remember: Populations with less variation are likely to go extinct! Cheetahs in Africa are one of the most extreme examples of genetic drift. The Cheetahs alive today are the descendants of only a few cheetahs. This means that Cheetahs are VERY genetically similar.They have lessresistance todisease and aremore likely to goextinct.Period 1, 6 stopped here 2/21/12
22Lizard Evolution on Islands shows genetic drift in action! keeps-ancestors-close/Period 2 stopped here 2/21/12
23Gene Flow: the movement of alleles into or out of a population Gene Flow: the movement of alleles into or out of a population. Immigrants add new alleles. Emigrants take alleles away Gene Flow Animation:
24Non-random Mating – when females prefer one phenotype over another Non-random Mating – when females prefer one phenotype over another. Also called sexual selection.Sexual Selection can cause sexual dimorphism: when males and females of the same species look noticeably different from each other
25Example of sexual selection: Peacocks Female peacocks prefer males with bright beautiful tails, so over time male peacocks have evolved to have very showy tails.Scientists have linked female preference to important traits such as health, size, and strength. In peacocks, scientists have linked tail size and color to nutrition.
26This means that females do not just want to mate with a male with a pretty tail for the look of him- females want to mate with males with pretty tails because they could have only produced this tail if he was able to find nutritious food. The female wants a male who is healthy enough to find food and can provide her offspring with nutritious food too.
27Sexual Selection and natural selection may often operate in opposing directions Males have traits like showy plumage in spite of their potential costs such as increased visibility to predators.
35A Mutation StoryWhat is the name of the deadly disease?What causes Malaria?How is having one mutated gene beneficial to Africans?How many genes does an individual need to have to express sickle cell anemia?How can a mutation be harmful in one environment and helpful in another?Why would a mutation persist if it kills people?Why are there more people with sickle cell anemia in one part of the world than in other parts?
36Allele Frequency and Sickle Cell Anemia Lab Weds-Thurs, Feb. 2/22-2/23
37Allele Frequency and Sickle Cell Anemia Background Info Read popcorn style!
38Friday, 2/24/12Warm-Up: Write down Table of Contents! Finish LAB!
39CHECK THE WEBSITE FOR ASSIGNMENTS!!! Go to STUDENTS CLASSES/HOMEWORK SCIENCE BIOLOGY!!!
40Why are alleles that are lethal in a homozygous individual maintained in the gene pool? (Use Sickle Cell and Malaria as an example.)
41Types of Selection and Hardy Weinberg Notes (Ch. 16.2) Monday, 2/27/12
42In Single- Gene Traits,… there are two phenotypes, whereas in polygenic traits, there are multiple phenotypes.Natural Selection acts differently on each of these.
43Is height a single-gene trait or a polygenic trait?
44Is Sickle Cell Anemia a single gene trait or a polygenic trait?
45Natural Selection on Single-Gene Traits can lead to… …changes in allele frequencies and therefore, evolution! This was shown in the Peppered Moth Simulation.
46Natural Selection on Polygenic Traits occurs in three ways: Disruptive SelectionStabilizing SelectionDirectional Selection
47Directional Selection When individuals at one end of the curve have a higher fitness than those at the other end.Examples: Finch bills, peppered mothsAnimation of Directional Selection:DA22_2/CDA22_2b/CDA22_2b.htm
48Stabilizing Selection When individuals near the center of the curve have higher fitness than individuals at either end of the curve- selection against both extremes.Examples: human baby size, lizard size, number of childrenAnimation of Stabilizing Selection:,00.html
49Disruptive SelectionWhen individuals at the lower and upper ends of the curve have higher fitness than those in the middle. This could cause the population to split into two distinct subgroups.Examples: duck bills, sexual dimorphism, sickle cell anemiaAnimation of Disruptive Selection:CDA22_2d/CDA22_2d.htm
50CA BIO STANDARD- Evolution Students know the conditions for Hardy-Weinberg equilibrium in a population and why these conditions are not likely to appear in nature.
51Hardy-Weinberg Principle Allele frequencies in a population will remain constant unless one or more factors causes those frequencies to change.When allele frequencies remain constant, it is called genetic equilibrium.If there is genetic equilibrium, evolution will not occur.
52Five conditions required to maintain genetic equilibrium: Random matingLarge populationNo movement into or out of the populationNo mutationsNo natural selection
53Conditions necessary for Hardy Weinberg Equilibrium /lab8/intro.html
54Animation of H-W Conditions h/life4e_15-6-OSU.swf
55Hardy Weinberg Equation Students know how to solve the Hardy-Weinberg equation to predict the frequency of genotypes in a population, given the frequency of phenotypes.
56Hardy Weinberg Cheat Sheet! Frequency of dominant allele = pFrequency of recessive allele = qThe sum of the two alleles in a population = 100%or…p + q = 1
57Hardy Weinberg Cheat Sheet! p2 + 2pq + q2 = 1p2 = frequency of AA homozygotes2pq = frequency of Aa heterozygotesq2 = frequency of aa homozygotes1 = frequency of all genotypes