14_352 - L ectu re 1 4 : G e n e t ic d r if t Todays...

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Lecture 14: Genetic drift Today s topics: 1. Random sampling error 2. Major results of drift 3. Special cases of drift Genetic Drift H-W assumes infinitely large population size, but real populations are finite, and subject to genetic drift . Genetic drift : “random sampling error of gametes” -> allele frequencies change due to random sampling
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The probability of a random event is only a theoretical expectation. Observed outcomes may differ from expectations due to random sampling error. Random Sampling Error Example: flip a coin 10 times. - The expectation is 5 heads and 5 tails, but what if you get 6 heads? - This is a 20% deviation due only to random sampling error. - If you flip 1,000 times, 20% deviation (600 H: 400 T) is very unlikely. (But 49% heads could easily happen!) - To be sure of getting exactly 50% heads, you need to flip an infinite number of times. Random Sampling Error
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The H-W theory states that p and q will not change over time, but this assumes an infinitely large population! Hardy Weinberg expectations
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This note was uploaded on 05/07/2011 for the course BIOLOGY 352 taught by Professor Townsend during the Spring '08 term at San Diego State.

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14_352 - L ectu re 1 4 : G e n e t ic d r if t Todays...

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