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Evolution Notes

CP Biology Ms. Morrison. Evolution Notes. Genes and Variation. Gene pool = combined genetic information of all members of a particular population Relative frequency = number of times allele occurs in a gene pool (usually %) 2 main sources of genetic variation:

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Evolution Notes

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  1. CP Biology Ms. Morrison Evolution Notes

  2. Genes and Variation • Gene pool = combined genetic information of all members of a particular population • Relative frequency = number of times allele occurs in a gene pool (usually %) • 2 main sources of genetic variation: • Mutations = change in DNA sequence, some change phenotype, some do not, can affect fitness or not • Gene shuffling = chromosomes moving independently from each other during meiosis and crossing-over, does not change relative frequency of alleles

  3. Genes and Variation, pg 2 • Number of phenotypes produced for a trait depends on how many genes control trait • Single gene – usually only 2 alleles so 2 phenotypes • Polygenic – several alleles, many genotypes and even more possible phenotypes, bell curve distributions common (normal distribution)

  4. Evolution = Genetic Change • Natural selection acts on phenotypes • Over time changes in relative frequencies of alleles • Leads to evolution

  5. Natural Selection in Polygenic Traits • Directional selection: individuals at one end of normal curve have higher fitness (shifts left or right) • Stabilizing selection: individuals in center of normal curve have higher fitness (curve narrows in middle) • Disruptive selection: individuals at each end have higher fitness than those in middle, can cause curve to split into two

  6. Genetic Changes • Genetic drift = particular allele changes frequency by chance, over time it can become common in the population • Founder effect = changes in allele frequencies when small subgroup of a population migrates to a new habitat • Hardy-Weinberg principle = allele frequencies remain constant unless one or more factors causes them to change

  7. Genetic Equilibrium • Alleles frequencies remain constant • 5 conditions required to maintain equilibrium • Random mating (equal opportunities to pass on alleles) • Large population (less effect from genetic drift) • No movement in or out of population (could gain or lose alleles otherwise) • No mutations (would result in new alleles) • No natural selection (no phenotype has selective advantage over another)

  8. Process of Speciation • Speciation = formation of a new species • New species evolve when populations become reproductively isolated from each other, 3 ways can happen: • Behavioral isolation – two populations have different courtship rituals or other behaviors • Geographic isolation – two populations separated by geographic barriers • Temporal isolation – two or more populations reproduce at different times

  9. Steps of Speciation • Founders arrive • Separation of population (do not go back to previous environment) • Changes in gene pool (result from adapting to new environment) • Reproductive isolation • Ecological competition (become more specialized for particular food source) • Continued evolution

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