What is a blood type? And the role of Genetics in it’s determination.
When we were little, I think in my 6th standard, some kinda medical camp happened at our school, and we were all told what our blood groups are! I was O+ and my sister happened to be B+ and we came back home and we found out my mum’s O+ and dad’s B+. Since then my sister kept on telling everybody that I got my mom’s blood and she got my dad’s, hence inherited all his afflictions. . 😅
I’ve heard her telling the same thing to a friend recently.. and I started digging deep into the details, what does it mean to have a particular blood type?! And do we inherit it from both the parents or just one of them?
We have all been taught, AB blood group can accept all other blood types, A guys can accept A and O, B guys B & O, and O guys can accept only O.(Oh Poor me, I used to think, but apparently, O+ constitutes the highest proportion of bloodgroups across the world!) And what’s the deal with +ve, -ve? I don’t remember reading about them at all in my biology class! 😅
Now let’s talk about what blood type even means! We all know our blood has RBCs. Along with RBCs, WBCs, Platelets and other stuff, there’s also Antibodies, and some protruding thingies on RBCs called Antigens. Your blood type is determined by what type of Antigens & Antibodies you have! Following table is self-explanatory.
Before I go any further.. notice the shape of antigens..circle and diamond, and the shape of the antibodies.(They totally look like pitch-forks to me 😂)
So the principle is, if antigen and antibody can fit into each other nicely, the blood starts clotting, and its a biiiiiig No! For example, Joe is A type and we pumped a litre of B into him.. what’ll happen next? Anti-B bodies in Joe’s body will fit nicely with freshly added B-blood and his blood starts clumping and it leads to an extremely serious condition called Acute hemolytic transfusion reaction and the worst case death!
Alternatively, imagine we pump a litre of O in his body though, O group doesn’t have any Antigens.. so no chance of forming clumps. He should be ok now! 🤓.
Wait a minute, I have talked about Os and As..what about the +ve and -ve parts of the BG? (oh yeah, that’s what i call blood group now!) Let’s just park that for a bit and talk about the interesting work of Genetics in determining why my sister is a B?!
Blood type is a trait determined by a single gene. Each of us has two copies of the gene for blood type on chromosome pair number 9. One copy is inherited from our mother, the other from our father. There are three versions (called “alleles”) of this gene: A, B, and O. A person’s blood type is determined by which allele he/she inherits from each parent.
So depending on which alleles you are inheriting from your mom and pop, your BG will be decided.
A & B alleles are co-dominant (hence AB group duh!), and O is recessive.
With his information in hand, let me map my family blood tree! (sounds sinsiter lol)
Based on our family blood types, I have written down the possible alleles. Mine and mum’s alleles are straight forward.. But my dad’s and my sister’s ain’t. They both could be BO or BB. Let’s talk about Sravani’s alleles first, she could only get O allele from my mum(cuz mum has only O alleles) . Hence BB isn’t a possibility.
Now that Sravani’s alleles are sorted, let’s move on to my dad’s. The answer lies in my blood group. Since I wouldn’t be a O bg, unless I get an O allele from my dad as well. So, that settles dad is a B bg with BO alleles.
Also, there’s a myth going around saying, you should definitely have one of your parent’s BGs! Not necessarily. Look at this beautiful example from wikipedia.
Here, the couple with blood groups A and B, and they can pass on their alleles in 4 different ways, and the kids might end up with O blood group or AB blood group which neither parents have! Nature, you tricky mistress! 😄.
(oh btw, the gender of the kids wont be determined by these alleles at all, i think they are just trying to have 2 boys & 2 girls in this illustration)
That’s enough information for today..! In next article I will cover the +ve and -ve parts of blood groups. It’s called Rh factor. Also, there are some very rare blood groups, and there’s a possibility that you will have a completely different bg, even if both your parents are O’s! I will cover these edge cases in another article.
Now go on and build your family trees as well! :)
Till next time! G
References:
https://en.wikipedia.org/wiki/ABO_blood_group_system
https://genetics.emory.edu/documents/resources/factsheet43.pdf
