Final answer:
A piece of chromosome that has lost its centromere is called a fragment. Sister chromatids, which are joined together at the centromere, separate when the centromere is lost.
Step-by-step explanation:
A piece of chromosome that has lost its centromere is called a(n) fragment. After DNA replication, each chromosome consists of two identical copies called sister chromatids, which are joined together at the centromere. When the centromere is lost, the sister chromatids separate, resulting in the formation of fragmented chromosomes.