Final answer:
A pair of chromatids consists of two identical copies of a chromosome joined at a centromere during cell division, visible when chromosomes condense and are essential for proper genetic inheritance.
Step-by-step explanation:
A pair of chromatids is comprised of two identical copies of a chromosome that are connected together at the centromere before a cell divides. During the S phase of interphase, DNA replicates, resulting in sister chromatids that are held together by cohesin proteins. When chromosomes are preparing to separate during cell division, they become more visible under a light microscope due to their full compaction and the constricted appearance of the centromeric region.
This is an integral step in the process of cell division, both in mitosis and meiosis, ensuring that each new cell inherits the correct number of chromosomes. These chromatids are visible just before cell division when the chromosomes condense and become more visually discrete. Each of the sister chromatids attaches to spindle microtubules at the centromere via a protein complex called the kinetochore.