Sometimes, when meiosis (the division of reproductive cells) occurs, chromosomes may be lost, left behind, or too many may be passed on, resulting in the birth of a child with a genetic defect or congenital or disease. One of the most common of these genetic disorders is Down syndrome. This disorder is named after Dr. Langdon Down, who was the first to formally describe it, in 1866. Down syndrome is a condition characterized by abnormal physical and mental development caused by a genetic defect. This genetic defect is caused by an extra chromosome. People born with Down syndrome have 47 chromosomes compared to the normal amount of 46, 23 chromosomes inherited from each parent. This extra chromosome originates more often in the mother's egg than in the father's sperm. Chromosomes are large, individual DNA molecules in the nucleus of a cell. They contain genes along with structures that hold DNA and help it express heredity by orchestrating cellular operations. Down syndrome is one of the most common chromosomal abnormalities and occurs in approximately 1 in 800 births. However, the frequency of the disorder varies greatly depending on the age of the mother. For women in their twenties the rate is 1 in 2,000, but quickly rises to 1 in 100 when a woman reaches her 40s. Down syndrome is usually recognized soon after birth due to characteristic facial features such as a flattened nose, upward tilt of the nose, eyes, a large tongue that often protrudes from a small...