A karyotype is the study of the chromosomes of an organism. For this, cells are removed and the cell division is stopped at a stage that allows to observe the chromosomes well. Modern techniques make it possible to see if genetic alterations exist and which ones.
The study of chromosomes is quite often used. As for example, during a pregnancy, if we fear a chromosomal abnormality in the future baby, a sample of some fetal cells can achieve a karyotype. This is done by removing fetal cells from the amniotic fluid (by amniocentesis), we can now sometimes perform this cell harvest by taking blood from the mother and extract fetal cells passed into the bloodstream of the mother. The karyotype makes it possible to study the chromosomes in the fetus and to search, for example, for trisomy 21.
Do all the cells of the same individual have the same genome?
Yes, all cells have the same genome, with a few details. However, it is not expressed in the same way. For example, insulin is only secreted by the pancreas while growth hormone is secreted by a gland called the pituitary gland, located in the brain. Because the genes, yet identically present in all cells, are ordered to be locked or to express themselves according to the cells in which they are located.
Author: Ladane Azernour Bonnefoy, geneticist.
Expert consultant: Professor Bernard Dujon, Pierre and Marie Curie University and Institut Pasteur (Paris).