Down syndrome (sometimes called Down's syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome — hence its other name, trisomy 21. This causes physical and mental developmental delays and disabilities.
Symptoms: Congenital heart defect
1. Down's Syndrome
Incidence: Occurs in approx.1 per 800 live births.
Chromosomal basis: Down syndrome is a genetic condition
that arises due to presence of an extra chromosome 21.
Here, chromosome 21 is repeated thrice (trisomy 21),
instead of showing up twice in a normal individual. The
karyotype of Down syndrome is represented as 47, XX,
+21 (females) and 47, XY, +21
The trisomic condition is usually caused by an error in the
process of cell division called non disjunction, i.e., inability
of chromosomes to separate at the time of cell division.
