A gene is a stretch of DNA (deoxyribonucleic acid), that codes for one or more traits in an organism. DNA is composed of four chemical bases whose sequences direct the production of specific proteins. The bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T).
Strands of DNA are bound to protein structures called chromosomes. Human cells contain twenty-three pairs of chromosomes or forty-six total chromosomes. One chromosome in each pair is inherited from each parent.
Therefore, each chromosome is composed of protein and a strand of DNA. A specific stretch of DNA is called a gene. The base sequence in each gene directs the production of a particular protein.
Example: Several stetches of DNA (genes) in human cells direct the production of different types of keratin proteins. Keratin proteins are found in hair, skin, and nail tissue. The genes that direct the production of keratin proteins are located on the DNA strands that make up chromosomes 12 and 17.