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Hardy-Weinberg Equilibrium Honors Biology

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Is evolution occurring right now? How might a scientist tell if evolution is occurring within a population?

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Use the Hardy Weinberg Equation!

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Review Mendel’s work Organisms have 2 alleles for each trait Only 1 can be passed to offspring This passing is requires alleles to separate in meiosis in a random fashion

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Gene Pools Collection of alleles within a population Ex: 1,000 cats Black (B) is dominant to white (b)

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Allele Frequency If governed by complete dominance, EX: 1,000 cats BB – black (360) = 36% Bb – black (480) = 48% Bb – white (160) = 16%

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Lets do some math With two alleles per cat, there are 2,000 alleles in the population If there are: 360 black (AA) = 720 B alleles 480 black (Aa) = 480 B alleles & 480 b alleles 160 white (aa) = 320 b alleles

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Allele frequencies: 1200 / 2000 B alleles exist (60% or 0.6) 800 / 2000 b alleles exist (40% or 0.4)

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If evolution is not occurring, The allele frequencies will not fluctuate over time Population is said to be at Hardy- Weinberg Equilibrium (HWE)

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H.W.E. Conditions 1. Very large population size 2. Isolation from other populations 3. No Mutations 4. Random Mating 5. No natural selection

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Applying H.W.E. p represents the dominant allele q represents the recessive allele p + q = 1 0.6 B alleles + 0.4 b alleles = 1

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Solve this story problem In certain Native American groups, albinism is due to a homozygous recessive condition. If the frequency of the allele for this condition is 0.06, what is the frequency of the dominant allele in this population? p + q = 1 P +.06 = 1 p =.94

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Applying H.W.E. (p + q) X (p + q) = p 2 +2pq + q 2 Male gametes Female gametes genotype frequencies in next generation

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Applying H.W.E. p 2 = homozygous dominant condition 2pq = Heterozygous condition q 2 = homozygous recessive condition p 2 +2pq + q 2 = 1 BB + 2Bb + bb = 1

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Solve this story problem In a certain flock of sheep, 4 percent of the population has black wool and 96 percent has white wool. If black wool is a recessive trait, what percentage of the population is heterozygous for this trait? p 2 +2pq + q 2 = 1 p + q = 1

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