what is t21

Trisomy 21, also known as Down syndrome, is a genetic condition caused by an extra chromosome. Most babies inherit 23 chromosomes from each parent, for a total of 46 chromosomes. However, in the case of Down syndrome, there is an extra copy of chromosome 21, resulting in a total of 47 chromosomes. This extra copy changes the typical development of the body and brain, leading to certain birth defects and learning problems. Down syndrome is not inherited in most cases, but it can be inherited in rare cases when the extra number 21 chromosome or part of it is attached to another chromosome in the egg or sperm, causing translocation Down syndrome. Another rare form is called mosaic trisomy 21, which occurs when an error in cell division happens after the egg is fertilized, resulting in both normal cells and some cells with an extra chromosome number 21.