Modern Evolutionary Biology I. Population Genetics A. Overview Sources of VariationAgents of Change MutationN.S. Recombinationmutation - crossing over - independent assortment VARIATION

G. Hardy and W. Weinberg Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions - Evolution: a change in the genetic structure of a population - Population: a group of interbreeding organisms that share a common gene pool; spatiotemporally and genetically defined - Gene Pool: sum total of alleles held by individuals in a population - Genetic structure: Gene array and Genotypic array - Gene/Allele Frequency: % of alleles at a locus of a particular type - Gene Array: % of all alleles at a locus: must sum to 1. - Genotypic Frequency: % of individuals with a particular genotype - Genotypic Array: % of all genotypes for loci considered; must = 1.

AAAaaa Individuals708050(200) Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions 2. Basic Computations

AAAaaa Individuals708050(200) Genotypic Array 70/200 = /200 =.4050/200 = 0.25 = 1 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions 2. Basic Computations

AAAaaa Individuals708050(200) Genotypic Array 70/200 = /200 =.4050/200 = 0.25 = 1 ''A' alleles /400 = 0.55 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions 2. Basic Computations

AAAaaa Individuals708050(200) Genotypic Array 70/200 = /200 =.4050/200 = 0.25 = 1 ''A' alleles /400 = 0.55 'a' alleles /400 = 0.45 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions 2. Basic Computations

- Determining the Gene Array from the Genotypic Array a. f(A) = f(AA) + f(Aa)/2 = /2 = =.55 b. f(a) = f(aa) + f(Aa)/2 = /2 = =.45 KEY: The Gene Array CAN ALWAYS be computed from the genotypic array; the process just counts alleles instead of genotypes. No assumptions are made when you do this. Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population 1. Definitions 2. Basic Computations

Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 1. Goal: Describe what the genetic structure of the population would be if there were NO evolutionary change – if the population was in equilibrium.

Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 1. Goal: Describe what the genetic structure of the population would be if there were NO evolutionary change – if the population was in equilibrium. For a population’s genetic structure to remain static, the following must be true: - random mating - no selection - no mutation - no migration - the population must be infinitely large

AAAaaa Initial genotypic freq Gene freq. Genotypes, F1 Gene Freq's Genotypes, F2 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example:

AAAaaa Initial genotypic freq Gene freq.f(A) = p =.4 +.4/2 = 0.6f(a) = q =.2 +.4/2 = 0.4 Genotypes, F1 Gene Freq's Genotypes, F2 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example:

AAAaaa Initial genotypic freq Gene freq.f(A) = p =.4 +.4/2 = 0.6f(a) = q =.2 +.4/2 = 0.4 Genotypes, F1p 2 =.362pq =.48q 2 =.16 = 1.00 Gene Freq's Genotypes, F2 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example:

AAAaaa Initial genotypic freq Gene freq.f(A) = p =.4 +.4/2 = 0.6f(a) = q =.2 +.4/2 = 0.4 Genotypes, F1p 2 =.362pq =.48q 2 =.16 = 1.00 Gene Freq'sf(A) = p = /2 = 0.6f(a) = q = /2 = 0.4 Genotypes, F2p 2 =.362pq =.48q 2 =.16 = 1.00 Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example: After one generation with these conditions, the population equilibrates

Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example 3. Utility: If no populations meets these conditions explicitly, how can it be useful?

Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 2.Example 3. Utility: If no populations meets these conditions explicitly, how can it be useful? For comparison, like a “perfectly balanced coin” AAAaaa Initial genotypic freq Gene freq.f(A) = p =.5 +.2/2 = 0.6f(a) = q =.3 +.2/2 = 0.4 HWE expections p 2 =.362pq =.48q 2 =.16 = 1.00 CONCLUSION:The real population is NOT in HWE.

Sources of VariationAgents of Change MutationN.S. RecombinationDrift - crossing overMigration - independent assortmentMutation Non-random Mating VARIATION So, if NO AGENTS are acting on a population, then it will be in equilibrium and WON'T change. Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 3. Utility: - if a population is NOT in HWE, then one of the assumptions must be violated.

-Also, If HWCE is assumed and the frequency of homozygous recessives can be measured, then the number of heterozygous carriers can be estimated. For example: If f(aa) =.01, then estimate f(a) =.1 and f(A) must be.9. f(Aa) = 2(.1)(.9) = Modern Evolutionary Biology I. Population Genetics A. Overview B. The Genetic Structure of a Population C. The Hardy-Weinberg Equilibrium Model 3. Utility: - if a population is NOT in HWE, then one of the assumptions must be violated.