A gene is the molecular unit of heredity of a living organism.[1] A genes consist of a stretches of deoxyribonucleic acid (DNA) that code for proteins that perform the necessary cellular functions in an organism.[2]:Glossary Genes are passed on to an organism's offspring so that its traits are inherited. Most biological traits are the combined effect of the actions of many genes. Some genetic traits are instantly visible, such as eye colour or number of limbs, and some are not, such as blood type, increased risk for specific diseases, or the thousands of basic biochemical processes that comprise life.