What is the primary characteristic of sister chromatids during cell division?

The primary characteristic of sister chromatids during cell division is that they are identical copies of a chromosome. This duplication occurs during the S phase of the cell cycle, where each chromosome replicates its DNA, resulting in two identical sister chromatids. These chromatids are joined together at a region called the centromere and play a crucial role during mitosis and meiosis. When the cell divides, the sister chromatids separate and are pulled to opposite ends of the cell, ensuring that each daughter cell receives an identical set of chromosomes. This uniformity is essential for maintaining genetic consistency from one generation of cells to the next.

In contrast to the other choices, pairs of homologous chromosomes refer to one chromosome from each parent, which are not identical but similar in shape and size. Chromatids that have not yet replicated would refer to the state before the S phase, and spindle fibers are structures that help separate the chromatids during cell division but are not characteristics of the chromatids themselves.