CBSE 2025, Compartment, Set 1

Question

A couple believed that hospital authorities have exchanged babies and they have been given another baby by them. The wife is blood group 'A', her husband is blood group 'B' and the child is blood group 'O'. 
(i) Could the baby be theirs ?
(ii) Justify your answer with the help of a cross.

Edvaya · Accepted Answer

The correct answer is Subjective. **SOLUTION** **(i) Yes**, the baby with blood group 'O' can absolutely be their biological child. **(ii) Justification using a Cross:** For a child to have blood group O, they must possess the homozygous recessive genotype ($ii$). This means they must have inherited one recessive allele ($i$) from each parent. Therefore, both the mother (Blood Group A) and the father (Blood Group B) must be heterozygous carriers. * **Mother's Genotype:** $I^A i$ * **Father's Genotype:** $I^B i$ **The Cross:** * Gametes of Mother: $(I^A), (i)$ * Gametes of Father: $(I^B), (i)$ **Possible Children:** * $I^A I^B \rightarrow$ Blood Group AB * $I^B i \rightarrow$ Blood Group B * $I^A i \rightarrow$ Blood Group A * $ii \rightarrow$ **Blood Group O** This cross clearly proves that heterozygous parents of blood groups A and B have a 25% chance of producing a child with blood group O.

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Biology > Reproduction And Genetics > Principles Of Inheritance And Variation

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