Understanding Chromosomes: The Building Blocks of Life Chromosomes are thread-like structures found in the nucleus of living cells that carry genetic information. They are composed of DNA tightly coiled around proteins called histones. Chromosomes come in pairs, with one inherited from each parent. In humans, there are 23 pairs of chromosomes, for a total of 46. The first 22 pairs are called autosomes, while the 23rd pair consists of the sex chromosomes (X and Y), which determine an individual's