This one is a confusion that I’ve heard people worrying about for so long that I feel I must share what I know with you on this matter. We all know our blood groups right? And how important they are for blood transfusion and stuff? Yeah. Well, people seem to think that when you have kids, you must have some “compatible” blood groups or you won’t be able to have kids or they’ll be abnormal. Even though I rarely use slang, this elicits just one response from me, always, dafuq?
First off, blood group is determined by our genes that decide the kind of sugar we have (or in case of group O, don’t have) on the RBCs (red blood cells). In our body, the genes code to form products that express themselves to make us like we are. There’s three alleles (variants/forms) of this blood group determining gene, viz., Ia, Ib and I which code for group A, B or no sugar (giving group O) respectively. The Ia and Ib show co-dominance while i is recessive, meaning, a person with IaIa or Iai is A, IbIb or Ibi is B, IaIb is AB and ii is O. We’re done with the overtly science-y stuff, promise.
So, as you can see, our genetic disposition determines our blood group. Many people have this notion that it is somehow related to having kids. Well, it isn’t. You can be of any blood group and still have perfectly normal kids. Their blood groups depend upon yours but nothing more than that.
When I tried to find out why people think this way, I realised it was because of erythroblastosis foetalis, a haemolytic disease due to which kids born to an incompatible mother are likely to die. This isn’t related to A/B/AB/O blood groups but to the presence or absence of Rh factor in your blood. Since I promised to stop being boring and forcing science on you, I’ll just tell you that this isn’t a problem these days as incompatible mothers (when kid is Rh positive and mother is Rh negative) are given RHOGAM injections and have successful deliveries free from complications; my sister and I are live examples.
Addendum: this thing’s just for fun. Here’s how to predict the blood groups if you know those of the parents (you can go the other way too but it’s a little difficult). From the parents’ blood groups you can tell their genetic composition (underlined above). Now, separate the two alleles in each parent (if IaIb then the two alleles are Ia and Ib). Finally make all possible combinations of mother’s alleles with those of the father and ta da! You have a probable chart of blood groups. I’ll give an example: if the mother is having blood group A and father is having blood group B then mother can be either IaIa or Iai and father can be IbIb or Ibi. So mom’s alleles are Ia or i and dad’s are Ib or i. So, kid can have Iai (where Ia from mom and i from dad) or Ibi (Ib dad and i mom) or ii (one i from each parent) or IaIb giving you equal chances of group A, B, O or AB. This is a rather difficult example for beginners. Usually the case is much easier, especially if you know the blood groups of the grandparents on both sides. I’ll be happy to solve any mystery that’s still left!