Microevolution

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Microevolution

• Chapter 16

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Overview

• Genetic Variation
• Genetic Equilibrium- a mathematical approach
• Microevolution

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Microevolution vs. Macroevolution

• Microevolution- changes in the frequencies of
  alleles of genes in a population
• Macroevolution- the process by which species and
  higher groupings of organisms originate, change,
  and go extinct

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Genetics Review

• Homologous Chromosomes?
• Alleles?
• Homozygous/Heterozygous?

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Variation in Populations

• Polymorphic Alleles
• Polygenic Traits

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Three Factors Determining Genetic Variability

• Rate of mutation
• Rate at which changes spread through a population
• Rate at which deleterious alleles are eliminated

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How Much Variation?

• About 1/4th of all human proteins have an
  alternate form present in at least 5 of the
  population
• 7 heterozygous for any human gene encoding a
  protein
• 1 in 500 nucleotides different
• All variation subject to natural selection?

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Hardy-Weinberg Equilibrium

• Allelic frequencies do not change from one
  generation from the next as long as
• 1) there is random mating
• 2) there is a large population size
• 3) there are no mutations
• 4) no breeding with other populations
• 5) no selection

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Hardy-Weinberg Example

• Mussels with two alleles (A and a) for color with
  blue being dominant
• Fraction of sperm or ova with A allele is p,
  fraction with a allele is q (p is 0.6)
• What genotypic frequencies will result from
  release of these sperm and eggs into seawater?

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How is this Helpful?

• Consider a genetic disease caused by a single,
  recessive gene
• 1 in 10,000 babies are born with this disease.
• What is the frequency of individuals who are
  carriers of this recessive allele?

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Non-Random Mating

• Positive assortative mating
• Negative assortative mating

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Random Drift

• affects small populations
• does not involve natural selection

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Gene Flow

• Increases the variation of a population into
  which genes are flowing
• Makes adjacent populations more homogenous

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Natural Selection

• Antibiotic-resistant bacteria becoming more
  common
• Cockroach traps baited with glucose cockroaches
  with aversion to glucose becoming more common