Science Questions

If I have B+ blood and so does my wife how can our son have O+ blood?

Kat -  Well, you’ll be asking the milkman what sort of blood group they have! No, this is all very simply explained. Blood group is determined by a set of genes. You get one gene each from your mum and one from your dad. Blood group’s determined by basically two different genes called A or B. You have certain versions of these and you can also get a version called O. These genes make proteins on the surface of your blood cells so if you have a gene that is A you make A proteins and they on the surface of your blood cells. If you have a gene for B that makes B proteins that go on the surface of your blood cells. If you have O then you don’t make any proteins. Going back to what I said about you having one gene from your mum, one from gene from your dad  - if you had one B gene and one O gene your blood group would be B because you’ve still got  a gene that’s making B proteins. Your blood cells are B. If you then were with someone else who had one B and one O and you had a baby with them your babies could either have BB genes, their blood group would definitely be B; they could be BO because they’ve one gene from you and maybe an O gene from mum or dad or they could have the two Os, in which case they would be blood group O. It’s perfectly possible to have two B parents having an O child from which you can actually infer both of you must be BO.

Chris -  That’s because group O is recessive.

Kat -  Exactly, group O is recessive because you have no proteins on the surface of your blood cells from this group. If you have even just one A or B gene that determines your blood type.

July 2008