The genetic disorder, Down's Syndrome is caused due to:

Trisomy of chromosome no. 21

The correct answer is Option (3) → Trisomy of chromosome no. 21

Down's syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. Instead of the typical two copies of chromosome 21, individuals with Down's syndrome have three copies, leading to a total of 47 chromosomes in their cells instead of the usual 46. Down's syndrome (Trisomy 21) affects both males and females because it is related to the gain of an autosome (chromosome 21) and not to sex chromosomes.The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.