AP BIOLOGY

Detailed explanation-1: -About 95 percent of the time, Down syndrome is caused by trisomy 21-the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.

Detailed explanation-2: -Abstract. Trisomy 21 (Down syndrome) is the most common autosomal trisomy in newborns, and is strongly associated with increasing maternal age. Trisomy 21 results most commonly from maternal meiotic nondisjunction. Unbalanced translocation accounts for up to 4% of cases.

Detailed explanation-3: -Down syndrome is also referred to as Trisomy 21. This extra copy changes how the baby’s body and brain develop, which can cause both mental and physical challenges for the baby.

Detailed explanation-4: -Down syndrome (trisomy 21) is a genetic disorder. It includes certain birth defects, learning problems, and facial features. A child with Down syndrome also may have heart defects and problems with vision and hearing.

Detailed explanation-5: -The most common is Standard Trisomy 21, in which the father’s sperm or the mother’s egg cell contains the extra chromosome.