Tuesday, January 1, 2013

Human Blood Groups & Civil Services :D !!

With advancement in modern medical interventions, where blood transfusion has become very important. Hence knowing a persons blood type is very important. 

There are more than 30 different blood typing, but we will learn the one most commonly used namely ABO Typing. There is another one called Rh factor but we will not cover it in this post. 

This system of blood typing classifies human blood into four types as shown above. These blood types basically differentiates different proteins on the top of Red Blood Cells(RBCs), so a person with A blood group will have a certain protein on its RBC and likewise. Remember O-blood group people do not have any proteins.  

Now if you observe that corresponding column shows the different genotypes. 

- IA and IB indicates dominant factor 

- i indicates submissive(called recessive) factor

These IA, IB and i are called alleles and they code for a certain trait in human body like eye colour, hair colour etc. In this case, these alleles are coding for the trait "Proteins on RBCs", which will ultimately determine which type of blood that human being will have. 

So, IA/IA says to have proteins type A on RBC, thereby meaning that person will have type A blood. IA/i also says the same i.e "to have protein A on RBC", as IA is the dominant one !! Same goes for other types of blood groups viz; B, AB and O. 
So, if question comes, if father has A type blood group and mother has B, what will the offspring blood group be? 

Let's draw the table to understand it. So seeing the genotype column above, we draw the following two possibilities.
So, we see that Father with A and Mother with B or vice-versa, can have offspring of all four types of blood groups viz; A, B, AB and O.  

So, lets solve this CSE 2011 Prelims Paper I question with above understanding. 
Q. A married couple adopted a male child. A few years later, twin boys were born to them. The blood group of the couple is AB positive and O negative. The blood group of the three sons is A positive, B positive, and O positive. The blood group of the adopted son is 
(a)  O positive 
(b)  A positive 
(c)  B positive 
(d)  Cannot be determined on the basis of the given data
 Ans: So using the genotype column from from above, we draw the following possibility.
In above table we have assumed father has AB and Mother has O. Even if you consider vice-versa, the answer would remain the same. 
So, above table shows that offsprings can have either blood group A or B. Hence the O+ has to be the adopted son. 

So you see remembering the genotype table above solves such blood type questions easily. 

Not just Civil Services, even CPF(AC) exam of 2011 has a question on blood type. 
Q. Father and mother having A and B blood group respectively
a) Cannot give birth to child with AB blood group
b) cannot give birth to child with O blood group
c) can give birth to child with O blood group
d) cannot give birth to twin child with B blood group  
We have solved this question above, with two possibilities, which certainly negates option A, B and D. 
So the right answer is option C


  1. cannot give birth to child with O blood group b is correct


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