A gene is a basic unit of heredity in living organisms. It is made up of DNA and carries the instructions for making proteins, which are essential for the structure and function of cells. Genes determine various traits, such as eye color and height, by influencing how an organism develops and functions. Genes are organized into structures called chromosomes, which are found in the nucleus of cells. Each species has a specific number of chromosomes, and humans have 23 pairs. Variations in genes, known as alleles, contribute to the diversity of traits within a population.