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Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium. What Darwin didn’t Get . Darwin couldn’t figure out why there was so much GENETIC VARIATION in natural populations. . Darwin thought that selection should ALWAYS favor the optimal form and eliminate vaiation…… hmmm…. But…….

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Hardy-Weinberg Equilibrium

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  1. Hardy-Weinberg Equilibrium

  2. What Darwin didn’t Get • Darwin couldn’t figure out why there was so much GENETIC VARIATION in natural populations.

  3. Darwin thought that selection should ALWAYS favor the optimal form and eliminate vaiation…… hmmm…. But…….

  4. The reality is, there is A LOT of variation in populations So how could this be?

  5. Hardy and Weinberg (1908) • Independently solved WHY this genetic variation exists • Hardy was a mathematician • Weinberg was a physician

  6. They showed that the frequency of genotypes in a population will stay the same from one generation to the next. That is if : SEVEN conditions are met We call this HARDY-WEINBERG EQUILIBRIUM

  7. THE BIG SEVEN Mutation is not occurring Natural selection is not occurring The population is very large All members of a population breed All mating is totally random Everyone produces the same number of offspring There is no immigration or emigration happening in the population

  8. Ok, so how realistic is this??? Not very, but we can use an equation as a model for population genetics • First you need to know that: • ALLELES represent GENES • Individuals receive one allele from each parent • This makes up an individuals genes • The genes determine the phenotype

  9. Therefore an individual will receive a combination of alleles in the form of : Dominant Dominant Recessive Recessive Dominant Recessive The alleles are represented as letters Capital letter = Dominant Lowercase Letter = Recessive AA aa Aa

  10. AA is called: HOMOZYGOUS DOMINANT • Aais called: HETEROZYGOUS DOMINANT • aa is called: HOMOZYGOUS RECESSIVE

  11. BREATH DEEP….here we go…… The HARDY- WEINBERG Equation (s) p + q = 1 p2 + 2pq + q2= 1 • These equations figure out: • ALLELE FREQUENCY • GENOTYPE FREQUENCY

  12. AA + Aa + aa = 1 p2 + 2pq + q2= 1 Formula for GENOTYPE Frequency

  13. A + a = 1 p + q = 1 Formula for ALLELE frequency

  14. Now that we know what each formula represents, figuring out each problem is easy!!!!!!

  15. You will ALWAYS be given That the characteristic is either DOMINANT or RECESSIVE Example: the problem will tell you that RED = R WHITE = r

  16. THEN you will be GIVEN A VALUE of one of these: A a AA aa And you already know that: A = p a = q AA = p2 Aa = 2pq aa = q2

  17. NOW all you have to do is.. Plug the values in!!! But it’s kind of like a maze Sooooooooo

  18. STEP 1: write out both formulas AA + Aa + aa = 1 p2 + 2pq + q2= 1 AND A + a = 1 p + q = 1

  19. Step 2: Figure out what you’ve been given and plug it in

  20. Example: if you are given the value of aa as 50% or .5o Plug .50 into the q2 spot AA + Aa + aa = 1 p2 + 2pq + q2= 1 p2 + 2pq + .50= 1 Now you can figure out q = .71 .50

  21. A + a = 1 p+ q = 1 P + .71 = 1 .29 + .71 = 1 AA + Aa + aa = 1 p2 + 2pq + q2 = 1 .084 + 2 (.29)(.71) + .50 = 1 .084 + .41 + .50 = 1

  22. Lets look at a problem The gene for an intelligent dolphin is dominant to a gene for an aggressive dolphin. In a population there are 25% that have the gene for homozygous recessive aggressiveness. Figure out the gene frequency for the heterozygous intelligent.

  23. OK, so we know that: We’re looking or GENE FREQUENCY Intelligent = A Aggressive = a Homozygous recessive = aa = 25% = .25 Heterozygous = Aa

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