PATHOLOGY

Detailed explanation-1: -Typically, a baby is born with 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. A medical term for having an extra copy of a chromosome is ‘trisomy.’ Down syndrome is also referred to as Trisomy 21.

Detailed explanation-2: -Most cases of trisomy 18 result from having three copies of chromosome 18 in each cell in the body instead of the usual two copies. The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 18.

Detailed explanation-3: -Also known as Down syndrome, trisomy 21 is a genetic condition caused by an extra chromosome. Most babies inherit 23 chromosomes from each parent, for a total of 46 chromosomes. Babies with Down syndrome however, end up with three chromosomes at position 21, instead of the usual pair.

Detailed explanation-4: -Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21. The type of error is called nondisjunction (pronounced non-dis-JUHNGK-shuhn).

Detailed explanation-5: -In Down syndrome, an individual most often inherits two copies of chromosome 21 from the mother and one chromosome 21 from the father for a total of three chromosomes 21 (Figure 3). Because Down syndrome is caused by the inheritance of three chromosomes 21, the disorder is also called trisomy 21.