A family has five girls and no son. Probability of son as the $6^{th}$ child will be

$(a)$ In humans, males are heterogametic and females are homogametic. Explain. Are there any examples where males are homogametic and females heterogametic ?

$(b)$ Also describe as to who determines the sex of an unborn child ? Mention whether temperature has a role in sex determination.

Assertion : In humans, the gamete contributed by the male determines whether the child produced will be male or female.

Reason : Sex in humans is a polygenic trait depending upon a cumulative effect of some genes on $X-$ chromosome and some on $Y-$ chromosome.

While solving the problem of sex determination in large number of insects, it was observed that

$A$ : $XO$ type sex determination is found in large number of insects.
$R$ : Some of the sperms bear the $X-$chromosome whereas some do not

A male child would be born to parents if