a medium-sized chromosome with one long and one short arm. The position of the centromere, which separates the p and q arms, is shown by the hatched area. This particular idiogram depicts the ...

1q21.1 microdeletion is “a chromosomal change in which a small piece of chromosome 1 is deleted in each cell,” according to MedlinePlus. “The deletion occurs on the long (q) arm of the ...