Final answer:
Chromosomes of cells grown in culture sometimes develop constrictions or gaps at particular locations called fragile sites, because they are prone to breakage under certain conditions.
Step-by-step explanation:
The constrictions or gaps that develop in chromosomes at particular locations are called fragile sites. These sites are prone to breakage under certain conditions. Fragile sites can result in chromosomal abnormalities and are often associated with genetic disorders.
One example of a fragile site is the common fragile site (CFS) FRA3B, which is located on chromosome 3. Breakage at this site is associated with the development of certain types of cancer, including lung and breast cancer. Other examples of fragile sites include the fragile X site on the X chromosome, which is associated with fragile X syndrome, and the FRA16D site, associated with a specific type of muscular dystrophy.