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NEETZoologyPrinciples of Inheritance and Variation

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): In a family where both parents are heterozygous carriers for sickle-cell anemia, if their first three children are unaffected, the probability that their fourth child will be affected is 1 4 . Reason (R): The fusion of gametes during fertilization is an independent event, and the genotypes of previ

Options

  1. ABoth Assertion (A) and Reason (R) are correct but Reason (R) is not the correct explanation of Assertion (A).
  2. BBoth Assertion (A) and Reason (R) are correct and Reason (R) is the correct explanation of Assertion (A).
  3. CAssertion (A) is correct but Reason (R) is incorrect.
  4. DAssertion (A) is incorrect but Reason (R) is correct.

Correct answer

B. Both Assertion (A) and Reason (R) are correct and Reason (R) is the correct explanation of Assertion (A).

Step-by-step solution

Sickle-cell anemia is an autosomal recessive disorder. If both parents are heterozygous carriers ( Hb^A Hb^S ), the cross is Hb^A Hb^S Hb^A Hb^S . The possible genotypes of the offspring are Hb^A Hb^A (normal), Hb^A Hb^S (carrier), and Hb^S Hb^S (affected) in a ratio of 1:2:1. The probability of having an affected child ( Hb^S Hb^S ) is 1 4 . Because each fertilization is an independent statistical event, the outcome of previous pregnancies does not change the probability for future pregnancies. The chance remains

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