Genetic Primer

Erik G. Puffenberger, Ph.D., Clinic for Special Children

The human body is composed of approximately 75 trillion cells. Groups of similar cells in the body are organized into tissues and organs (e.g. liver or kidney) which have specific functions (e.g. digestion, respiration, and circulation). However, all cells, no matter what their function in the human body, contain the full complement of genetic material that we call DNA. DNA is a chemical component of every cell that acts as the blueprint for growth, development, and regulation of all aspects of body chemistry.

What is DNA?

Deoxyribonucleic acid (DNA) is the hereditary material of the human body. DNA is made up of four different chemical compounds, namely adenine (A), guanine (G), cytosine (C), and thymine (T). These four chemicals are linked together into a long string. Within each cell in the body, these strands of DNA exist in a very ordered fashion, namely as chromosomes.

What is a chromosome?

Each cell contains 46 very long strands of DNA that are called chromosomes. Both the egg and sperm carry half the normal complement of chromosomes (i.e. 23). Once fertilization occurs, the new embryo contains a full set of chromosomes (46), half (23) derived from the father and half (23) from the mother. However, these chromosomes are not all different. The chromosome set inherited from the mother contains the same chromosomes as the set from the father. Thus, while each cell carries 46 chromosomes, there are two copies of each chromosome per cell. As an analogy, imagine the chromosomes as a 46-volume set of encyclopedias. The complete set is composed of two identical 23 volume sets. One 23-volume set is inherited from the father and the other from the mother. Thus, there are two copies of volume 1, two copies of volume 2, etc.

What is a gene?

A gene is a discrete section of DNA which has a specific function. Each gene is encoded by a specific and unique portion of DNA on a chromosome. Genes are the blueprints for manufacturing the materials that the body requires in order to function properly. Every protein and enzyme found in the human body is produced from the instructions found within the genes. It is estimated that there are approximately 50,000 genes found on the human chromosomes.
Based upon the encyclopedia analogy, each page in the set of encyclopedias would carry the instructions for a single gene. Since there are two copies of each volume in the set of encyclopedias would carry the instructions for a single gene. Since there are two copies of each volume in the set of encyclopedias, then it follows that there are also two copies of every page (and thus, two copies of every gene). These encyclopedias, however, are not written with the usual 26-letter alphabet, but rather try a simpler four letter alphabet, corresponding to the four chemical compounds which make up DNA (A, G, C, and T). Thus, a page torn out of one of these books might read like:
….ATGCTAGACCATCAGACTATTCCGTATTGA…

To get more information on how a gene is read, and the different types of genetic mutations, please click here, and you will be linked to a PDF. To return to the DDC Clinic web site, click the back button on your browser.