It's something to do with the fact that having sickle cell anaemia reduces the chances of contracting malaria, obviously a very common disease in Africa. I'm not quite sure what the link is but hopefully this helps a little bit?
<em>During dna replication, the enzyme dna polymerase adds new nucleotides to the </em><em>3</em><em>'</em><em> end of the sugar in the growing strand</em>
