SCD AND MALARIA - PowerPoint PPT Presentation

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SCD AND MALARIA

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    1. SCD AND MALARIA ALLISON

    2. POLYMORPHISM Occurrence together in the same habitat of two or more discontinuous forms of a species in such frequencies that the rarest of them cannot be maintained by recurrent mutation A and S alleles AS heterozygote - to 40 % East Africa 0.1 mutation/gene/generation to replace S by recurrent mutation = inexplicable

    3. BALANCED POLYMORPHISM One allele has a selective advantage until a certain gene ratio is established p[A] + q[S] = p2[AA] + 2pq[AS] + q2[SS] Heterozygote [AS] has an advantage over either homozygote AA - sensitive to malaria = fitness 0.95 AS - resistance to malaria = fitness 1.19 SS - high mortality = fitness 0.30

    9. HYPERENDEMIC MALARIA Transmission of Plasmodium falciparum continues throughout the greater part of the year - constantly re-infected Severe and prolonged disease before immunity - infant mortality - 200 - 500/1000 - age of maximal susceptibility and mortality from malaria