Final answer:
An a-centric fragment is a piece of a chromosome that has lost its centromere. It arises due to a deletion and cannot be properly segregated during cell division, leading to potential genetic disorders or cell death.
Step-by-step explanation:
A piece of a chromosome that has lost its centromere is called an a-centric fragment. This type of fragment is generated when there is a structural alteration in the chromosome, such as a deletion. The centromere is essential for the movement and segregation of chromosomes during cell division, and without it, the a-centric fragment cannot properly align or be distributed to daughter cells. As a consequence, such a fragment may be lost during the cell division process, potentially leading to various genetic disorders or cell death. When a chromatid loses its centromere, it can no longer be pulled to opposite poles during anaphase because it lacks the kinetochore structure that microtubules attach to.