UPSC Prelims 2011·GS1·science-and-technology·science and technology

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

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Last updated 23 May 2026, 3:31 pm IST
  1. AO positiveCorrect
  2. BA positive
  3. CB positive
  4. DCannot be determined on the basis of the given data

Explanation

To solve this, we look at the genetics of blood groups. The mother has blood group O negative, meaning her genotype is OO and she is Rh negative. The father has blood group AB positive, meaning his genotype is AB and he is Rh positive. When an OO parent and an AB parent have children, the possible genetic combinations for the offspring are AO or BO. This means their biological children can only have blood group A or blood group B. It is biologically impossible for a couple with blood groups AB and O to produce a child with blood group O. This is because the AB parent will always pass on either an A or a B gene, and group O requires two O genes (one from each parent). Since the three sons have blood groups A positive, B positive, and O positive, the son with blood group O positive must be the adopted one. Therefore, the correct answer is A.
science-and-technology: A married couple adopted a male child. A few years later, twin boys were born to them. The blood group of the couple is
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