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Evolution Notes

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Western University
Biology 3466B
Yolanda Morbey

Evolution NotesDec 2011 Germ theory 1858 and theory of natural selection 1859 happened at the same time In London in 1854 there was an outbreak of cholera John Snow mapped deaths and locations of pumps The broad street pump was causing the cholera so once it was removed cholera cleared up This was the beginning of modern medicine Origin of modern medicine Cholera outbreak in London 1854 Louis Pasteur and the germ theory of disease 1858the idea that disease are caused by microorganisms Joseph Lister and antiseptic surgery 1865 Alexander Fleming and the discovery of penicillin 1928 There was an initial decline in tb death rates starting in the early 1900s due to improved housing sanitation conditions and nutrition The final decline in tb was due to antibiotics Streptomycin and isoniazid were antibiotics that helped to remove tb even more This represents the impact of the discovery of antibiotics used to treat tb Flu virus evolution The influenza A virus has ten genes on eight strands of RNA Neuraminidase N and hemagglutinin H are surface proteins They are recognized and remembered by the host immune system There are five antigenic sites on H that are most important for immune systemhost recognition Mutations in antigenic sites make the virus unrecognizable to the host which results in evolution of the virus The pathogen and host are in an evolutionary arms race The pathogenvirus needs the host in order to reproduce and the host has mechanisms to combat it immune system They are in a constant battle Molecular evolution in flu virus Surviving virus lineages had 77 substitutions at antigenic sites Extinct lineages had 47 substitutions at antigenic sites Most mutations and eventually substitutions are happening at antigenic site of H and this confers greater virus survival Evolution is occurring rapidly at antigenic sites as part of the evolutionary arms race with the host immune system If H is under positive selection how should the slope differ from the slope for a gene subject to drift alonewill be greater Clinical implications The surviving flu lineage usually has the most amino acid replacements in its H antigenic sites Mutations in 18 codons seem to be under positive selection Is evolution of the H gene consistent with the neutral theoryNo genetic drift is not the dominate mechanismmethod of evolution at this gene Origin of pandemic flu strains A phylogeny of the nucleoprotein gene is shown and it is responsible for host specificity what kind of host the virus is able to infect Can be horse human or pig Pandemic years were 1918 1957 1968 Sometimes swine is present within human lineages The H3N2 of 1968 is in a clade where all others are H1 and H2 so where did H3 come from The phylogeny of the H gene shows that all horses have H2 and H4 is only present in the avian clade Humans are diverged from within the avian clade and H3 in humans came from an avian source Origin of 1918 flu H1N1 1910 is the estimated year when the common ancestor of human and swine influenza lived Human and swine strains have common origin The origin of the 1918 strain is unknown Human and swine clade doesnt arise within any other clade and the sequence data for H1N1 from 1910 from other hosts is not available The human clade is most closely related to swine strain Human and pigs strains likely descended from 1918 flu or its close relative There is no definitive answer to origin on 1918 H1N1 There is no data It could have been swine grouped closely with humans or avian transfer H1N1 easily to other hosts Origin of swine flu What caused highly virulent strain in 2009 Believe H1N1 emerged in 1918 in humans likely from avian H1N1 there was crossspecies transmission H1N1 went extinct in 1958 The human population was resistant to it a different form outcompeted it It reappeared in 1977 from swine likely due to contamination from lab source The classical H1N1 swine is responsible for
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