My_Ch23_lecture(2009030423565699)

My_Ch23_lecture(2009030423565699) - Chapter 23 Evolution of...

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Chapter 23: Evolution of Populations Purpose —to understand the factors that influence how populations evolve (= population genetics). You MUST understand the principles of the Hardy-Weinberg equilibrium, and be able to do the calculation. (AP Themes are the same as Ch 22) What you MUST know in Ch 23: Gene pool Hardy-Weinberg equilibrium Altering genetic composition (Hardy-Weinberg) Advantage of heterozygosity Types of selection (directional, disruptive, stabilizing) There isn’t much, if anything that you don’t need to know in this chapter…Hint! Better know this! Gene pool —the total genes (allele frequencies) in a population at any one time Genetic drift —changes in the gene pool due to random chance (random increase or decrease of alleles) In small populations, genetic drift exerts a strong influence on evolutionary changes Gene flow —transfer of alleles between populations due to immigration, emigration, or movement of gametes (plants), which can change the gene pool Natural selection —differential survival and reproductive success of those best adapted to the environment Hardy-Weinberg equilibrium
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The 5 conditions required to maintain Hardy-Weinberg genetic equilibrium give the conditions for NO EVOLUTION occurring: 1. Large population size (no genetic drift) 2. Isolation from other populations (no gene flow) 3. No mutations (mutations alter the gene pool) 4. Random mating (individuals do not choose mates with certain inherited traits) 5. No natural selection (traits are selectively neutral) According to the H-W equilibrium, if any of these do NOT occur, you will get evolutionary change. So….if you have: 1. genetic drift 2. gene flow 3. mutation 4. nonrandom mating 5. natural selection these are the processes that cause microevolution. This concept is frequently lost in the process of doing the H-W calculations. Calculation of the H-W equilibrium : On virtually every standardized test that asks you to calculate this, they will use the same ratios/percentages. Look at Cliff’s or other review books, work through the problems, and be aware of the numbers in the examples— the numbers will always be such that you can do the square root of p 2 or q 2 in your head ! It’s just too painful for them to not have round numbers for the answer. Practice doing these problems, until it becomes obvious to you how easy they are to figure out! This is EASY math , and virtually the only math you need to know! If:
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p = frequency of 1 allele (for example R, for red flowers) q = frequency of the other allele (r) p 2 = frequency of homozygote RR q 2 = frequency of homozygote rr 2pq = frequency of heterozygotes (pq + qp, or Rr + rR) Then the following 2 equations hold: 1. p + q = 1 (the sum of all alleles = 100%) 2.
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