(N/A) In humans,the total number of chromosomes is $23$ pairs $(46)$. Out of these,$22$ pairs are autosomes and $1$ pair consists of sex chromosomes.
Chromosomal disorders are primarily caused by the failure of segregation of chromatids during cell division,leading to gain or loss of chromosomes (aneuploidy).
$1$. Autosomal disorders: These involve abnormalities in the $22$ pairs of autosomes. $A$ classic example is $Down's$ syndrome,which is caused by the presence of an additional copy of chromosome number $21$ (Trisomy of $21$).
$2$. Sex chromosomal disorders: These involve abnormalities in the sex chromosomes ($XX$ or $XY$). Examples include:
- $Klinefelter's$ syndrome: Caused by the presence of an additional $X$ chromosome in males $(47, XXY)$.
- $Turner's$ syndrome: Caused by the absence of one $X$ chromosome in females $(45, X0)$.