Genetics 101

By Rados, Carol | FDA Consumer, November-December 2005 | Go to article overview

Genetics 101


Rados, Carol, FDA Consumer


Each person has a unique set of chemical blueprints that determine how his or her body looks and functions. These blueprints are contained in their own deoxyribonucleic acid, or DNA, which is made up of two twisting sequences or single strands that are able to be paired with another.

Each single-stranded DNA fragment is made up of four different coding molecules, or base pairs, called nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C) that are linked end to end. Each base on the opposite strand specifically pairs with, or is the complement of, the other: an A always pairs with a T, and a C always pairs with a G. A DNA molecule with the sequence A-T-T-G-C, for example, will stick to or complement another with the sequence T-A-A-C-G to form a double-stranded DNA. This sequence, or the order of these pairs, spells out the exact instructions for creating an organism, such as the human genome, with its own unique traits, or genetic code.

Specific segments of DNA that contain the instructions for making specific body proteins, such as those that determine the physical features of blue eyes or curly hair, are called genes. Other DNA segments provide the instructions for the body to produce important chemicals called enzymes that help to direct and control the chemical reactions that occur within the body. Depending on the codes of a specific gene, even a small error within the DNA structure sometimes can mean serious problems for the entire body. An error in just one gene can even result in a shortened life.

Genes are found in specific segments along the length of human DNA, neatly packaged within structures called chromosomes. …

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