Microevolution and Changing Alleles (The Hardy-Weinberg Principle) (Chap. 19)

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Microevolution and Changing Alleles (The
Hardy-Weinberg Principle)(Chap. 19)

• Know from text population, gene pool, population
  genetics, allele frequency

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Hardy Weinberg Principle/Equation

• In genetics, frequency refers to a proportion or
  percentage
• both the allele and genotype frequencies will
  remain unchanged (genetic equilibrium) unless
  outside forces change those frequencies.
• can be used to test for natural selection
• if allele and genotype freq. in a pop. are in
  equilibrium for a particular gene, natural
  selection (among other things) is not affecting
  the population and there is no evolution happening

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Rationale behind HW Principle

• What are the probabilities of obtaining various
  gametic combinations?
• prob. of A from male A from female
• pm x pf p2
• prob. of a from male a from female
• qm x qf  q2
• prob. of A from male a from female, or a from
  male A from female    
• (pm x qf ) (pf x qm ) 2pq
• What is the result of the binomial expansion of p
  q in males females
• (pm qm) (pf qf) p2 2pq q2

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• p frequency of dominant allele
• q frequency of recessive allele
• the sum of the frequencies of the alleles within
  a population must always equal 1
• p q 1
• ex. A a 1
• the sum of genotypes must also equal 1.
• p2 2pq q2 1
• p2 freq. of AA genotype
• 2pq freq. of Aa genotype
• q2 freq. of aa genotype
• ex) AA Aa aa must total 1

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Restrictions of the Hardy-Weinberg Principle

1. mating is random
2. no mutation
3. no immigration nor emigration
4. alleles must segregate (Mendels first law)
5. population and sample are infinitely large
6. no natural selection operating on the population