When the chromosome number of a given organism has one additional chromosome in one of the homologous pairs,the condition is known as . . . . . .

Find out the correct pair.

Three copies of chromosome-$21$ in a child with Down's syndrome have been analysed using molecular biology technology to detect any possible $DNA$ polymorphism with reference to different alleles located on chromosome-$21$. Results showed that out of $3$ copies,$2$ of the chromosomes of the child contain the same alleles as one of the mother's alleles. Based on this,when did the non-disjunction event most likely occur?

Match List-$I$ with List-$II$ : Choose the correct answer from the options given below :

List-$I$	List-$II$
$A.$ Down's syndrome	$I.$ $11^{th}$ chromosome
$B.$ $\alpha$-Thalassemia	$II.$ $X$ chromosome
$C.$ $\beta$-Thalassemia	$III.$ $21^{st}$ chromosome
$D.$ Klinefelter's syndrome	$IV.$ $16^{th}$ chromosome

Edward syndrome is on account of .......

$A$ male individual with $47$ chromosomes due to the addition of an $X$ chromosome suffers from a condition called: