Chromosomes
Chromosomes are thread-like structures made up of DNA (deoxyribonucleic acid) molecules and proteins. They are found in the nucleus of every cell and carry the genetic information of an organism. The full content of chromosomes varies depending on the species. Humans, for example, have a total of 46 chromosomes, organized into 23 pairs. Each chromosome consists of a single, long DNA molecule tightly coiled and condensed around proteins called histones. The DNA molecule contains genes, which are segments of DNA that provide instructions for building and functioning of the body. Genes determine various traits and characteristics, such as eye color, hair texture, and susceptibility to certain diseases. The DNA molecule itself is composed of nucleotides, which are the building blocks of DNA. There are four types of nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). These nucleotides pair with each other in a specific manner—A with T and C with G—to form a double he...