Genetics Overview

What is a gene?

To understand what genes are, it is helpful to know where they are in the body. Our bodies are made of cells. These cells are fluid filled sacs that are so small you cannot see them with just your eye. You would need a microscope. However, when many of them are together they make a tissue you can see. For example, your skin is one type of tissue. Within almost every cell of the body there is another even smaller structure called a nucleus. This is where the genes are found. There are about 25,000 genes in the nucleus. These 25,000 genes don’t float around loosely in the cell. They are packaged in a line in structures called chromosomes to keep them organized. Thus, a chromosome is just a very long string of thousands of genes plus some other genetic material. There are 23 pairs of chromosomes. The reason they come in pairs is so that each of us can inherit one from each of our parents. In this way, we get half of our chromosomes from our mother and half from our father. Genes are made of DNA. DNA, which stands for Deoxyribose Nucleic Acid, is the body’s instruction code. Simply, it is a series of just four base pairs – adenine (A), guanine (G), thymine (T), and cytosine (C). The order of the bases sends a message much like a sentence. For example, the code may read AAGTACCATGA… The genes provide all the necessary instructions to make proteins for our growth and survival. The order of these base pairs doesn’t differ very much from one person to the next. In fact, the order is the same 99.9% of the time. However, that .1% difference is why people are different. Some of the differences are what makes us have or be prone to certain diseases.