Monosomy of what causes down syndrome?
Monosomy of what causes down syndrome?
The male sex has one X and one Y chromosome. The female sex has two X chromosomes. Turner syndrome is a genetic condition caused by an abnormality on one of your sex chromosomes. It's also called monosomy X, gonadal dysgenesis, and Bonnevie-Ullrich syndrome.
Causes ; 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.
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, 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. Occasionally, the extra chromosome 21 is attached to another chromosome in the egg or sperm; this may result in what is called "translocation" Down syndrome (3 to 4 percent of cases). This is the only form of Down syndrome that can sometimes be inherited from a parent. Some parents have a rearrangement called a balanced translocation, where the #21 chromosome is attached to another chromosome, but it does not affect his/her health. 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.
Causes ;
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.
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, 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. Occasionally, the extra chromosome 21 is attached to another chromosome in the egg or sperm; this may result in what is called "translocation" Down syndrome (3 to 4 percent of cases). This is the only form of Down syndrome that can sometimes be inherited from a parent. Some parents have a rearrangement called a balanced translocation, where the #21 chromosome is attached to another chromosome, but it does not affect his/her health. 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.
