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What evidence do studies of human genome diversity provide about the…

- - - - novel alleles confer advantage against pathogens evading normal allele.
    - - HLA class I diversity naturally increases with distance away from East Africa.
      - Despite this, virus richness has a positive correlation with HLA diversity with distance from African taken into account.
      - PDBS pathogen driven balancing selection hypothesis
        
        The greater the diversity of pathogens, the higher the HLA diversity of a population compared to average
      - HLA B was demonstrated to have higher diversity than HLA A and C because B gene is under higher selective pressure by pathogens.
  - - - purifying selection
        
        Duffy blood group, DARC gene fixation
        
        DARC encodes red blood cell chemokine receptor, Fy
        
        DARC alleles
        
        FY*A
        
        FY*B
        
        FY*O
        
        No Fy expressed
        
        Underdominant
        
        FY*O homozygotes less but not complete susceptibility to vivax malaria
        
        FY*O homozygotes do have lower mortality if both vivax and falciparum malaria co-infect host.
      - deleterious allele: alleles that reduced selective fitness
    - - balancing selection
        
        Sickle cell anaemia
        
        Beta globin anaemia
        
        Beta & alpha globin thalassaemias
        
        GLucose-6-phosphate dehydrogenase
        
        depletion of RBCs but inhibits parasite infection.
        
        SCL4AQ ovalocytosis in heterozygotes
        
        homozygotes fatal
        
        Cystic fibrosis
        
        delta F508 allele where phenylalanine 508 is deleted from CFTR.
        
        CFTR chloride ion channel is target of bacterial toxins such as vibrio cholera
      - maladaptive
        
        CCR5 chemokine receptor acts as cofactor for entry of HIV into cell.
        
        Europe CCR5delta32 is a 32bp deletion leading to frame shift.
        
        CCR5 no longer produced leading to underdominance
- - - - ABO shows balancing selection
    - - Affects calcium signalling to disrupt parasite growth