Interviewee: Matt Ridley. The ABO gene codes for an enzyme called galactosyl transferase and determines your blood group. In people with A and B blood groups, the gene differs by seven basepairs, four of which have an effect on the type, shape and activity of the enzyme. People with O blood group have a single deletion in the gene that causes an inactive protein to be made. (DNAi Location: Genome > Tour > Genome spots > Chromosome 9, blood groups > A chromosome 9)

On chromosome 9 are the blood groups – the A, B, O blood groups which are relevant to blood transfusion. Why are people different? Some people have A blood, some people have B blood, some people have O blood. Well, it turns out that this variation in the human population might have something to do with a past history of infectious diseases. People with O blood are more susceptible to cholera, for example. People with AB blood are particularly resistant to cholera. Perhaps past epidemics have left their traces in human populations by giving us different patterns of genes.

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