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Genetics 101


Genetics and genetic testing are complicated subjects. The following will give you an overview. You may want to explore other web sites as well. The National Institute of Health's publication,  "Understanding Gene Testing" is a good resource.

The National Human Genome Research Institute has a useful glossary of genetic terms with pictures. During your appointment, we will explain genetic concepts in more detail and answer your questions. Below is a brief lesson in "Genetics 101."

Our bodies consist of millions and millions of cells. Genetic material, or DNA, is stored inside each. The DNA is organized into 46 packages, called chromosomes. Genes are simply pieces of information carried on the chromosomes. Cells use genes like instructions to make proteins they need to function. Human beings are thought to have 30,000 to 35,000 genes, divided among the chromosomes in each cell. The DNA that genes are made of is like a code written with only four letters. Sometimes misspellings (mutations) happen in a gene. Extra letters may be inserted into the code. Letters may be missing. Or one letter is found where another ought to be. Sometimes, but not always, these mutations can cause disease.

Most of our chromosomes come in pairs, like the genes they carry. One copy of each gene comes from our mother and one from our father. Some genetic diseases are caused when there is a mutation in both copies of a gene. These are called "recessive" conditions. Cystic fibrosis and sickle cell anemia are examples of recessive diseases. Other genetic diseases occur when there is a mutation in only one copy of a gene. These diseases are "dominant" conditions. Marfan syndrome is an example of a dominant condition. Some genetic diseases are much more complex. They are caused by the combination of more than one gene mutation and the environment. Cardiovascular disease, asthma and most common cancers are examples of complex genetic diseases.

Genetic tests identify genetic mutations or the signs that a mutation may be present. Some genetic tests involve checking a gene's DNA code "letter by letter" to find a mutation directly. When this isn't practical, less direct methods are used. For example, genetic tests may look at the proteins made by a gene to see if they are normal in size or other characteristics. Some genetic tests look at the bigger picture. Such biochemical tests look at the role of the enzymes and proteins that are encoded by our genes. Several tests done for genetic risk of heart disease are biochemical tests.