Answer to Question #90239 in Cell Biology for Darian

Question

Down syndrome, the most common genetic condition in the United States, is also called trisomy 21. What does this mean?

Answer 1

When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby will have a complete set of 46 chromosomes, half from the father and half from the mother.Sometimes, an error occurs when the 46 chromosomes are being divided in half, and an egg or sperm cell keeps both copies of the 21 chromosome instead of just one copy.If this egg or sperm is fertilized, then the baby will have three copies of the 21 chromosome, which is called trisomy 21, or Down syndrome. The features of Down syndrome are caused by that extra copy of chromosome 21 being in every cell in the body.