How Does Mosaicism Happen in Down Syndrome?
Mosaic mean skin#
Because skin cells and brain cells arise from the same type of cell at the beginning of fetal development (ectoderm), many doctors believe that skin cell tests reflect the chromosomal makeup of the brain cells as well. When mosaicism is suspected but not confirmed through the blood test, other cell types may be tested: skin and bone marrow are most commonly the next cells checked. In the latter case, it may be more difficult to diagnose mosaicism. While mosaicism can occur in just one cell line (some blood cells have trisomy 21 and the rest don't), it can also occur across cell lines (skin cells may have trisomy 21 while other cell lines don't). However, this blood test can only determine the level of mosaicism in the blood cell line. If some of the cells have trisomy 21 and some don't, then the diagnosis of mosaicism is made. The usual way in which mosaic Down syndrome is discovered is through genetic testing of the baby's blood. In Down syndrome, mosaicism means that some cells of the body have trisomy 21, and some have the typical number of chromosomes. When a person has more than one type of chromosomal makeup, that is called mosaicism, like the mosaic style of art in which a picture is made up of different colors of tiles. (All like cells originating from a single type of cell is called a cell line for example, the skin cell line, the blood cell line, the brain cell line, etc.)
From then on, all cells originating from that cell will have the different chromosomal number, unless another mistake happens. However, mistakes sometimes happen and one cell ends up with a different number of chromosomes.
After fertilization, the zygote then proceeds to divide.Īs new cells form, the chromosomes duplicate themselves so that the resulting cells have the same number of chromosomes as the original cell. Every cell in the human body comes from one initial cell: the fertilized egg, which is also called the zygote.