KCET · BIOLOGY · STD 12 - 4. Principles of Inheritance and Variation

The offspring produced from a marriage have only O or A blood groups. Of the genotypes given below, the possible genotypes of the parents would be

A \(I ^{ A } I ^{ A }\) and \(I ^{ O } I ^{ O }\)
B \(I ^{ A } I ^{ O }\) and \(I ^{ O } I ^{ O }\)
C \(I ^{ A } I ^{ A }\) and \(I ^{ A } I ^{ O }\)
D \(I ^{ O } I ^{ O }\) and \(I ^{ O } I ^{ O }\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(I ^{ A } I ^{ O }\) and \(I ^{ O } I ^{ O }\)

Step-by-step Solution

Detailed explanation

(B) \(I ^{ A } I ^{ O }\) and \(I ^{ O } I ^{ O }\),
For the offspring to have only A or O blood group, at least one parent must carry the \(I ^{ O }\) allele, and the other must carry \({I }^{ A }\).
Among the given options, possible parental genotypes are \(I ^{ A } I ^{ O }\) (A blood group) and \(I ^{ O } I ^{ O }\) (O blood group). It can be shown with the help of following cross:

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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