Down Syndrome – August 28, 2002

Down Syndrome – August 28, 2002

Normally, chromosomes reside in the cell nucleus, totaling 46, or 23 pairs, one of which is the sex chromosome. Chromosomes are the primary basis of genetic information. Sperm contributes 23 chromosomes, and egg also contributes 23 chromosomes, and the fertilized egg absorbs both, bringing the total chromosome count to the usual 46, or 23 pairs. However, fertilized eggs formed through close relatives, drug abuse, severe infectious diseases, or immune deficiencies may have 47 chromosomes—either too many sperm or too many eggs can lead to this situation. When this happens, infants exhibit Down syndrome, characterized by abnormal facial expressions, unusual physical features, and intellectual disability.