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Bio2 Lecture 21

Bio2 Lecture 21 - Bio2 Lecture 21 Population Genetics...

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Bio2 Lecture 21 4/7/05 Population Genetics & Microevolution - Hardy-Weinberg Equation - Departures from Hardy-Weinberg Equilibrium - Stabilizing, Directional and Disruptional Change Evolution is a process of adaptation (def: modifications that improve fitness) to the environment. Natural selection acting on VARIATION , (preserving if beneficial, removing if detrimental) is the means by which this process regulates Microevolution – Short-term small-scale adaptations of populations to changes in the environment; result of a change in allele frequency. (beetle getting a thicker cuticle to become immune to pesticides). Macroevolution – Long-term large-scale changes above the species level. Population – all the individuals of the same species living in a particular area at the same time. Share a common gene pool . Gene Pool – the sum of all alleles of all genes in a population. Genotype - alleles Phenotype - expression of genotype Allele Frequency – must always add up to 1, because it defines the gene pool, must be 100%. If allele frequency doesn’t change there is no change going on, (A = 0.9, a = 0.1) Frequency stable genetic equilibrium , if they do change, then we do have micro level evolution Frequency change evolution Alleles haploid, genotype always diploid A = 0.9 a = 0.1 Dominant allele A frequency = p Recessive allele a frequency = q Use punnet square - Genotype AA (homozygous dominant) o Frequency = p^2 o P^2 = 0.81 - Genotype frequency = aa o Frequency – q^2 o Q^2 = 0.01 - Genotype Aa (heterozygous) o Frequency = p*q
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o P*q = 0.09 Hardy-Weinberg Equation - Describes a population in equilibrium (not evolving) - P^2 + 2pq + q^2 = 1 - P^2 = freq of AA - Q^2 = freq of aa - 2pq = freq of Aa - 1 = all the individuals in a population - How many people are carriers of albinism? o We know albinism is recessive q o 1 in 20,000 are albinos q^2 o Therefore…. . o If q^2 = 1/20000 then q = 1/141 o And p = 140/141, p + q = 1 o P^2 + 2pq + q^2, we are looking at 2pq o So we know 2pq = 2(140/141)(1/141) 1/70 or 1.4% o Now we can tell you the Heidy-Weinberg we can tell what the rate is, but we wont know what the cause is - What proportion of mouse population will have white coats if:
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Bio2 Lecture 21 - Bio2 Lecture 21 Population Genetics...

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