Does Your Child Have Down Syndrome? What Is Down Syndrome? Down Syndrome is a genetic disorder in which one has an extra chromosome that causes developmental as well as intellectual delays. Every normal individual has 46 chromosomes. A chromosome comprises of genetic material that determines how a baby's body is formed during pregnancy & how the body grows & functions during pregnancy and after birth. Down Syndrome occurs when there is an abnormal cell division that results in an additional partial or full copy of the 21st chromosome which can originate from either parent. This extra genetic material from chromosome 21 is responsible for the distinctive facial appearance, intellectual disability and developmental delays.