NEET 2025 — Biology solution

NEET2025Biology

With the help of given pedigree, find out the probability for the birth of a child having no disease and being a carrier (has the disease mutation in one allele of the gene) in F $_{3}$ generation.

A
Zero
B
$\frac{1}{4}$
C
$\frac{1}{2}$
D
$\frac{1}{8}$

Solution

From the pedigree, a carrier female (F1) crossed with an unaffected male produced an affected male child in F2. This pattern points to a sex-linked recessive trait.

For the F3 cross, the parents are a carrier female ( $X^{c} X$ ) and an affected male ( $X^{c} Y$ ). The Punnett square is:

	$X^{c}$	$Y$
$X^{c}$	$X^{c} X^{c}$ (affected female)	$X^{c} Y$ (affected male)
$X$	$X^{c} X$ (carrier female)	$X Y$ (unaffected male)

Out of the 4 possible offspring, only 1 ( $X^{c} X$ ) is disease-free and a carrier.

$∴$ Required probability $= \frac{1}{4}$ .

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