Science Questions

You were discussing the A,B,O blood group system a little while ago and explained that A and B dominate type O. What about the Rhesus blood group system? Is there a dominant one for that? Carter, US

Sarah -  The rhesus blood typing system is very similar to the A, B, O system, but it's much more complicated.  There's not just three types, it's actually a lot.  When people talk about Rhesus positive or Rhesus negative they're talking about the Rhesus D gene.  That means that you either have or do not have these particular structures on the outside of your red blood cells.  Rhesus positive means that you do have them and Rhesus negative means that you don't have them.  He's exactly right that Rhesus positive is dominant.  The allele for that is dominant over the Rhesus negative allele.  Actually about 84% of the UK population is Rhesus positive.

Ben -  So that again (as with the A, B, O system) means that if you have two parents that are Rhesus negative then you're certainly going to be Rhesus negative, but if your parents are Rhesus positive then actually you could turn out to be either.

Sarah -  Yes. Both of my parents are Rhesus positive but I'm Rhesus negative.

Ben -  That means we can work out that each of your parents has one copy of the gene saying Rhesus positive and one saying Rhesus negative in order to have passed on the negative ones to you.

Sarah -  Yep!

August 2008