When does sex determination occur in humans?

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

In the buccal cavity slide cell of an individual, we observe a dark-stained body near the nuclear membrane. The genotype of the individual may be

$A$ family has five girls and no son. What is the probability of having a son as the $6^{th}$ child (in $\%$)?

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.

In our society,women are often blamed for giving birth to daughters. Can you explain why this is not correct?