Science Questions

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

Sun, 27th Jul 2008

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Bieran De Saille asked:

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


Kat -  Well, youíll 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 groupís 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 donít 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 youíve still got  a gene thatís 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 theyíve 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. Itís perfectly possible to have two B parents having an O child from which you can actually infer both of you must be BO.

Chris -  Thatís 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.


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Biren Desai asked the Naked Scientists: I have B+ Blood and my wife has also B+ group. But I wonder my son has O positive group, How? What do you think? Biren Desai, Sat, 21st Jun 2008

Don't file for divorce Biren... RD, Sat, 21st Jun 2008

Each of you will have two genes for ABO grouping. O genes don't express a protein, A and B express the A and B proteins respectively.

So if each of you has an O and a B gene, you'll both have B-type blood, but you'll each pass on only one gene (either O or B) to your baby so if both of you happen to hand on the O gene the baby will have O type blood (25 % chance), if one of you passes on an O and one a B gene the baby will have B type blood (50 % chance) or you might both pass on a B gene (25 % chance) the baby will have B type blood. rosy, Sun, 22nd Jun 2008


Same case here that Mine & mine wife is having the same blood group B+, and our daughter is having the O+.

I understood here that this could be either B or O, I want to know that whats is approx. probability of B & O globally and also if you can tell what would be for Indian cases.

Hitendra Bhatia hitendra_bhatia, Sun, 29th Jun 2014

Here is a list of the prevalence of various blood types around the world.

O+ is one of the most common blood types.  B+ a little less so.

As far as your chance of having an O+ child. 

The A, B, and Rh+ genes are essentially dominant. 

If you and your husband are B+, then you could either be:

B/B or B/O  and either Rh+/Rh+ or Rh+/Rh-

Since your child is O+, we know that both you and your husband are B/O.  We don't know which Rh genes you express.

So, if you have another child, then it could be:

BB  (both maternal and paternal B, (B phenotype))
BO  (maternal B, paternal O (still B phenotype)
OB (maternal O, paternal B (B phenotype)
OO (maternal O, paternal O)

So, each of your children has a 75% chance of being B, and a 25% chance of being O.

If either or both parents are Rh+/Rh+, then 100% of your children will be Rh+. 
If you both have Rh+/Rh-, then as above, the child has a 75% chance of being Rh+, and a 25% chance of being Rh-.

If you both have a recessive Rh- gene, and a recessive O gene, then chances of having an O- child will be 1/4 x 1/4 = 1/16 , or 6.25%. CliffordK, Mon, 30th Jun 2014

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