Are chromosomal abnormalities, such as monosomy or trisomy, confined only to certain parts of the body?

Question

Some examples of the abnormalities I'm talking about result in Down's Syndrome (extra chromosome 21), Turner's Syndrome (only one X chromosome), Klinefelter's syndrome (an extra X chromosome), and Monosomy 7 (absent chromosome 7).

Answer 1

Not typically. The egg or sperm has an extra or missing chromosome so all the cells after replication do too. It is possible to have mosaicism, in which a monosomy or trisomy arises or resolves sometime during development. Mosaicism is sometimes detected during amniocentesis or CVS which can complicate diagnosis a bit. In some cases phenotype might be more mild for mosaic individuals, but the abnormal cells are not typically confined to specific body part or organs. You don't get Turner syndrome in your left foot, for example.

Answer 2

Chromosomes are found in all cells of the body that contain a nucleus. Since all our cells come from an original progenitor cell that carried the chromosomal aberration, all cells will contain the abnormality. However, not all cells function in the same way. Thus the abnormalities only manifest themselves in those areas that require expression of the genes found in the damaged chromosomes.

Answer 3

No, those chromosomes experienced nondisjunction during meiosis when the gametes were being made. That means that the abnormality was in the zygote (fertilized egg) from which all other body cells arose. So all cells in the body have this same abnormality.

It isn't like a skin cancer where UV light changed genes in skin cells, but other cells are not affected.