BILD 3 Lecture Notes - Lecture 7: Genetic Drift, Bild, Macroevolution
13 Jun 2018
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BILD 3 Lecture 7
4/16/2018
• Evolution
o Is genetic change over time
• Macroevolution
o Is change in the composition of species over time
o Macroevolution=mutation, gene flow, genetic drift, natural selection + billions of
years
o Reconstructed using all evidence such as geology, fossils, and living organisms
• Microevolution
o The change in gene frequency within a population over a short period of time
o Most easily observed in species with
▪ Short generation time
▪ Very large population at each generation
▪ Ex: bacteria
• Dr. Alexander Flemming
o Looking for antibacterial agents for staph infection for soldiers from WWI
o Mold grew on a plate and inhibited the growth of staph→plate was
contaminated with a fungus, named Penicillin (1929)
o Did’t yet know if it could fight infections in humans: first human patient was
Albert Alexander in 1941→Ernest Chain and Howard Florey administered 5 days
of the drug
o Chain, Florey, and Flemming shared the Nobel in 1945
o By 1943, Penicillin was mass produced for WWII: beginning of antibiotic era
o In 1947, the first Penicillin resistant pathogen was identified
o 1961: first documented strains of MRSA
• natural selection is just one way populations can differ from HW: other ways are genetic
drift and gene flow
• genetic drift (not all of the population can /does reproduce)
o two are’t true of HW assuptios: populatios are’t always large, ad ot
everyone has a chance to breed
o is the change in the genetic composition of a population caused by chance
events unrelated to fitness, but can cause a population to evolve
o why does it happen
▪ because of sampling error: by chance, the population sample in the next
generatio does’t reflect the prior frequencies
▪ random events, like a volcano eruption or only green bugs getting
stepped on as opposed to brown
o the smaller the sample, the more chance for sampling error, and therefore,
there’s a higher chace of geetic drift i a sall populatio
o when not all of the population can /does reproduce, the frequencies of alleles
gets skewed
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