What Causes Down Syndrome?
What causes Down syndrome?
Normally in reproduction, the egg cell of the mother and the sperm cell of the father start out with the usual number of 46 chromosomes. The egg and sperm cells undergo cell division where the 46 chromosomes are divided in half and the egg and the sperm cells end up with 23 chromosomes each. When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby ends up with a complete set of 46 chromosomes, half from the father and half from the mother.
In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped the objects called chromosomes.
Down syndrome is usually caused by an error which 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, the baby ends up with three copies of the #21 chromosome and this is called “trisomy 21” or Down syndrome. The features of Down syndrome result from having an extra copy of chromosome 21 in every cell in the body.
Ninety-five percent of Down syndrome results from trisomy 21. Rarely, a form of Down syndrome called “mosaic” Down syndrome may occur when an error in cell division occurs after fertilization (1 to 2 percent of cases). These persons have some cells with an extra chromosome 21 and others with the normal number.
- what is down syndrome?
- down syndrome learning and development
- down syndrome health issues
- down syndrome pre-natal diagnosis
- down syndrome genetic testing
- down syndrome diagnostic tests
- down syndrome babies
- down syndrome children
- trisomy 21
- down syndrome pictures
- down syndrome symptoms
- mosaic down syndrome
