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When and how does a population change genetically?

When and how does a population change genetically?. An accelerated biology introduction to Hardy-Weinberg. Equilibrium.

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When and how does a population change genetically?

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  1. When and how does a population change genetically? An accelerated biology introduction to Hardy-Weinberg

  2. Equilibrium • The frequency of alleles (dominant, recessive) in a population REMAIN in equilibrium unless an external pressure acts upon them or they are a very small population and change by chance. • PRESSURE: • NATURAL SELECTION: forced selection • SEXUAL SELECTION: mate choice • GENE FLOW: • Immigration: Alleles enter a population • Emigration: Alleles exit a population

  3. Two Equations must be used to determine the genotypic and allele frequencies in a population. • Genotypic Frequencies: • p2 + 2pq + q2 = 1 • AA + Aa + aa = 1 • Allele Frequencies: • p + q = 1 • A + a =1 • Genotypic frequencies can change in a population that is not evolving but allele frequencies must remain the same. How can this be true?

  4. Sample question The historical allele frequencies for a population of rainforest frogs that exhibit the recessive trait albinism is: .8 dominant allele and .2 recessive allele You are sent out to study if the allele frequency is changing. You count 50 white frogs and 650 green frogs. Is this population in equibrium? Mathematically show why or why not!

  5. Followup: What might you conclude about the frogs you studied? In a population of frogs in equilibrium, the amount of white frogs can change from one generation to the next. How can the population of frogs be in equilibrium, yet you see a change in the number of white frogs?

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