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Hardy Weinberg or Not? An Introduction to How Microevolution Can Act on Alleles in a Population Questions for Discussion What do Dominant and Recessive Mean? Six Fingers is dominant…why do most of us have 5? Why do many Northern Europeans carry the lethal recessive CF allele? Are these alleles stable or is selection occurring? Gene Pool Gene pool is the total aggregate of genes in a population at any one time. Population is a localized group of individuals belonging to the same species. Species is a group of populations whose individuals have the potential to interbreed and produce fertile offspring.* Hardy-Weinberg Theorem The frequencies of alleles and genotypes in a population’s gene pool remain constant unless acted on by a force other than segregation and recombination. (eg. Meiosis and random fertilization do not affect a gene pool) Equation: p2 + 2pq + q2 = 1 p2 + 2pq + q2 = 1 Represents: AA, A, aa p + q =1 – How many genotypes? How many phenotypes? This is known as the allele frequency. Is the allele frequency the same at the genotype frequency? Why or why not? First step—always figure out WHAT you know for certain! Simple Problem: Suppose Red is Dominant and White is recessive in flowers. If 96% of the flowers are red, what are the frequencies of the individual genotypes in the population. p2 + 2pq + q2=1 p+q=1 To Start: What do we know for certain? Allele frequencies remain in equilibrium if (Must be true to be IN EQUILIBRIUM) Very large population. No migration. No net mutations. Random Mating. No Natural Selection. In Small Populations Alleles can be selected for/against by chance! Genetic Drift: Bottleneck Effect Founder effect Migration=Gene Flow How does migration effect allele frequency? Immigration Emigration Sexual Selection=Nonrandom mating What does the data suggest about who Drosophila females find “sexy” Let’s use the equation to see if a population is in equilibrium: You study a population of frogs in a river system in Colorado. In the parent generation the allele frequencies are p=.67 and q=.33; You analyze the phenotypes tadpoles produced and you note that: 11/100 are homozygous recessive. Is this gene at Hardy-Weinberg Equilibrium. What can you infer about population size and mating habits of the frogs in this population? Long term data You continue to look at the allele frequencies in this population of frogs for every year for 10 years. At the end of 5 years, the allele frequencies are p=.67 and q=.33 At the end of 10 years p=.5 and q=.5 What may have happened to this population? Microevolution is… Changing allele frequencies. Our Model: Goldfish eating Sharks! How does natural selection alter allele frequencies. Over time…what can microevolution do? Which might lead to speciation Which might lead reduced variability?