A couple, both carrying the gene for sickle cell anaemia, is planning to get married. What are the chances of having anaemic progeny?

The correct option is D $25\%$
couple planning to get married carrying gene for sickle cell anaemia.

suppose, ${XX}^s$ female x ${XY}^s$ male

	X	$X^s$
X	XX	X$X^s$
$Y^s$	X$Y^s$	$X^s$$Y^s$

$X^s$$Y^s$ 25% , X$Y^s$ 50% , XX 25% normal

only 25% chances of having anaemic progeny.

Thus, the correct answer is D.