Target Exam

CUET

Subject

Biology

Chapter

Principles of Inheritance and Variation

Question:

The probability of having a haemophilia carrier daughter by a haemophilia carrier mother and a normal father is:

Options:

100%

50%

25%

75%

Correct Answer:

25%

Explanation:

The correct answer is Option (3) → 25%

Hemophilia is an X-linked recessive disorder. A carrier mother has one normal X chromosome and one hemophilia-carrying X chromosome (XhY). A normal father has one normal X chromosome and one normal Y chromosome (XY).

Cross Analysis:

When we cross the genotypes, we get four possible combinations for their children:

  1. X (from father) and X (from mother) → XX (normal daughter)
  2. X (from father) and Xh (from mother) → XhX (carrier daughter)
  3. Y (from father) and X (from mother) → XY (normal son)
  4. Y (from father) and Xh (from mother) → XhY (hemophilic son)

Probability Calculation:

Out of these four possibilities:

There is one carrier daughter genotype XhX out of the total four possible outcomes.

So:

  • Probability of having a carrier daughter = \(\frac{1}{4}\) = 25%