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Evolution - PowerPoint PPT Presentation

Evolution. Hardy-Weinberg Principle. I ntro. Last day we left off talking about populations… Populations geneticists are able to quantify the total number of alleles within a population == this is known as the gene pool

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Presentation Transcript

Evolution

Hardy-Weinberg Principle

Intro

• Last day we left off talking about populations…

• Populations geneticists are able to quantify the total number of alleles within a population ==this is known as the gene pool

• They are able to accomplish this by measuring each allele frequency, which is the proportion of gene copies in a population for a given allele

• Therefore evolutionary changes in populations can be quantitatively measured by looking for changes in allele frequencies

Example

Hmmm…

• In terms of evolution, would the dominant form of a moth wing become more and more common over time?

• Do allele frequencies remain constant or change over time?

• These questions were answered independently (think Darwin vs. Wallace) by a mathematician named Hardy and physicist named Weinberg== thus Hardy-Weinberg principle

The Principle

• Allele frequencies will not change over time (generation-generation) if the following conditions are met:

• The population is very large

• Mating opportunities are equal

• No mutations occur

• No migration occurs

• All individuals have an equal chance at reproductive success==no natural selection

Equation

• The H-W-P is often expressed using the following equation (for a gene with only 2 alleles==A/a):

• let p=frequency of A and q=frequency of a, then

p+q=1

(p+q)2= 1

p2 + 2pq + q2 = 1, where

p2= frequency of AA; 2pq= frequency of Aa; and q2 = frequency of aa

Moth example

Note: genotype frequencies will remain the same from generation to generation as long mating is random

Pgs 547-549

Pg 549 PP’s #1-3

Quiz Tomorrow

-self quiz

-review #1-4, 7, 8, 10, 15