Final answer:
A chromosome is a structure within a cell's nucleus made up of DNA and proteins. When unwound during cell growth phases, these complexes are called chromatin. Chromosomes become tightly coiled and visibly distinguishable during cell division.
Step-by-step explanation:
A chromosome is a structure found within the nucleus of a cell, which is made up of DNA and proteins. These DNA-protein complexes take on different forms based on the phase of the cell cycle. During the growth and maintenance phases, these complexes appear as unwound, jumbled bunches of threads known as chromatin. When a cell is preparing to divide, the chromatin becomes more tightly coiled and condenses into the distinguishable chromosomes. Chromosomes are encoded with genetic information organized into units called genes.
Upon DNA replication, each chromosome consists of two identical copies, called sister chromatids, which are held together at a region known as the centromere. It is during cell division that the chromosomes become more visibly distinguished, often absorbing different dyes to reveal characteristic banding patterns under a microscope.