In Turner syndrome,a female has:

Loss or gain of a segment of $DNA$ results in

Given below are two statements :
Statement $I$ : Down's syndrome is caused by the absence of one of the $X$-chromosomes.
Statement $II$ : Turner's syndrome is caused by the presence of an additional copy of the chromosomes.
In the light of the above statements, choose the correct answer from the options given below :

Turner's syndrome in humans is caused by

$A$ chromosome complement with $2n-1$ is called as:

Which disorder is caused by autosomal primary non-disjunction?