What do visible chromosomes consist of?

Visible chromosomes during cell division consist of two identical sister chromatids. This structure forms when DNA is replicated during the S phase of the cell cycle, resulting in two copies of the chromosome, each known as a sister chromatid. These sister chromatids are initially joined at a region called the centromere.

As a cell prepares to divide, these chromatids become condense and visible under a microscope. The visibility of chromosomes is primarily observed during phases of mitosis or meiosis, where they take on a characteristic X-shaped appearance due to the close alignment of the sister chromatids. This ensures that during cell division, each daughter cell receives an identical set of chromosomes.