Exam 2 Study Guide - Plagues

Exam 2 Study Guide - Plagues - Exam II Study Guide The Red...

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Exam II – Study Guide The Red Queen Hypothesis : sex is needed to keep “one step ahead” of parasites that cause disease. Need to be able to recombine and maintain a set of genes that code for defenses, e.g. extra mucous, more effective T-cells. Maintaining Diversity: Sexual species carry a storehouse of “defenses,” This backup comes in 2 forms: Heterozygosity - when an organism carries two different forms of a gene, Polymorphism - when a population carries many different forms of a gene. Cystic Fibrosis: Normally, mucus works to move microbes out of lungs, CF causes thick mucus, and clogs air passages, Interferes with pancreas. Heterozygosity and cystic fibrosis: Humans carry two alleles for a gene, when alleles combine, it determines what trait will develop, Mendelian – Dominant alleles produce the traits they carry even if recessive allele is present, but 2 recessive alleles will produce recessive trait. Heterozygosity, sickle cell anemia and malaria: Human sickle gene - may be defense against malaria, Hemoglobin is a molecule that transports oxygen in the blood, single allele mutation changes a small part of the molecule. Human sickle gene - may be defense against malaria. Heterozygous infants: 1 normal and 1 sickle allele (AS) = more resistant to malaria, Homozygous people with no sickle allele are very susceptible to malaria (AA) Homozygous people with both alleles “sickle” are anemic (SS) and do not live long. Resistance genes & computer games: Modeling sex and disease , which is more “fit” in terms of evolution: sexual or asexual reproduction? Started with a population of 200 SIMS , 100 sexual; 100 asexual , Sexual population always died out - sexual reproduction is more difficult, conclusion? Made model more complex, SIM-pathogens with “virulence” genes could kill SIM- hosts, SIM-hosts given “resistance” genes; Sexual population won game when disease was present. Real world?: Topminnows - Usually sexual, but may reproduce asexually, Get blackspot disease, caused by a parasitic protozoan Asexual populations much more blackspot than the sexual ones. Rabbits overrun Australia: European rabbits introduced to Australia (1859) Overran rangeland - major pest. Looked for solution, European rabbits in South America, Native rabbits in South America, virus. Myxomatosis: Virus deliberately introduced to Australia in 1950, Highly lethal (ca. 99.9%), Next year mortality at 90%, In 7 yrs, mortality dropped to 25%, 1965 - 1/5 as many rabbits lived in Australia as had been there prior to 1950. Co-evolution of host and pathogen: Remember virgin soil epidemics , New pathogen encounters a naïve population , Disease highly lethal , In small, disbursed population epidemic may quickly die out , In large, dense populations, epidemic may come in waves , Stable disease pattern can develop only if both host pop. and pathogen pop. survive the initial encounter. Virulence moderation: Microbes can evolve much more quickly than humans - generation times so short, Microbes adjust much more quickly in new
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Exam 2 Study Guide - Plagues - Exam II Study Guide The Red...

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