| Genes - the chemical messages of heredity - | | | | exception of mature red blood cells, which have no |
| constitute a blueprint of our possibilities and limitations. | | | | nucleus) contains the same DNA. Each cell has 46 |
| The legacy of generations of ancestors, our genes | | | | molecules of double-stranded DNA. Each molecule is |
| carry the key to our similarities and our uniqueness. | | | | made up of 50 to 250 million bases housed in a |
| When genes in genetic testing are working properly, | | | | chromosome. |
| our bodies develop and function smoothly. But should | | | | The DNA in each chromosome constitutes many |
| a single gene - even a tiny segment of a single gene | | | | genes (as well as vast stretches of noncoding DNA, |
| - go awry, the effect can be dramatic: deformities | | | | the function of which is unknown). A gene is any |
| and disease, even death. | | | | given segment along the DNA that encodes |
| In the past 20 years, amazing new techniques have | | | | instructions that allow a cell to produce a specific |
| allowed scientists of genetic testing to learn a great | | | | product - typically, a protein such as an enzyme - |
| deal about how genes work and how genes are | | | | that initiates one specific action. There are between |
| linked to disease. Increasingly, researchers are able to | | | | 50,000 and 100,000 genes, and every gene is made |
| identify mutations, changes within genes that can | | | | up of thousands, even hundreds of thousands, of |
| lead to specific disorders. In genetic testing tests for | | | | chemical bases. |
| gene mutations make it possible not only to detect | | | | Human cells contain two sets of chromosomes, one |
| diseases already in progress but also, in certain | | | | set inherited from the mother and one from the |
| situations, to foresee diseases yet to come. That is | | | | father. (Mature sperm and egg cells carry a single set |
| called Genetic Testing. | | | | of chromosomes.) Each set has 23 single |
| This new ability raises both high hopes and grave | | | | chromosomes - 22 autosomes and an X or Y sex |
| concerns. On the one hand, predictive genetic testing | | | | chromosome. (Females inherit an X from each parent, |
| holds out the possibility of saving thousands of lives | | | | while males get an X from the mother and a Y from |
| through prevention or early detection. On the other, | | | | the father.) |
| the implications of test results are enormous, not | | | | For a cell to make protein, the information from a |
| only for the individual but also for relatives who share | | | | gene is copied, base by base, from DNA into new |
| this genetic testing legacy, and for society as a | | | | strands of messenger RNA (mRNA). Then mRNA |
| whole. | | | | travels out of the nucleus into the cytoplasm, to cell |
| This article of Genetic Testing presents key concepts | | | | organelles called ribosomes. There, mRNA directs the |
| and issues relevant to genetic testing and answers | | | | assembly of amino acids that fold into completed |
| questions that are frequently asked about the | | | | protein molecule. |
| techniques, potential risks, and possible benefits of | | | | Each human cell contains 23 pairs of chromosomes, |
| attempts to link genetic markers with disease. | | | | which can be distinguished by size and by unique |
| WHAT ARE GENES IN GENETIC TESTING? | | | | banding patterns. This set is from a male, since it |
| In Genetic Testing Genes are working subunits of | | | | contains a Y chromosome. Females have two X |
| DNA. DNA, which carries the instructions that allow | | | | chromosomes. Different genes are activated in |
| cells to make proteins, is made up of four chemical | | | | different cells, creating the specific proteins that give |
| bases. Tightly coiled strands of DNA are packaged in | | | | a particular cell type its character. |
| units called chromosomes, housed in the cell's nucleus. | | | | HOW DO GENES WORK IN GENETIC TESTING? |
| Working subunits of DNA are known as genes. DNA | | | | Although each cell contains a full complement of DNA, |
| is a vast chemical information database that carries | | | | cells use genes selectively. Some genes enable cells |
| the complete set of instructions for making all the | | | | to make proteins needed for basic functions; dubbed |
| proteins a cell will ever need. Each gene contains a | | | | housekeeping genes, they are active in many types |
| particular set of instructions, usually coding for a | | | | of cells. Other genes, however, are inactive most of |
| particular protein. | | | | the time. Some genes play a role in early |
| DNA exists as two long, paired strands spiraled into | | | | development of the embryo and are then shut down |
| the famous double helix. Each strand is made up of | | | | forever. Many genes encode proteins that are unique |
| millions of chemical building blocks called bases. While | | | | to a particular kind of cell and that give the cell its |
| there are only four different chemical bases in DNA | | | | character - making a brain cell, say, different from a |
| (adenine, thymine, cytosine, and guanine), the order in | | | | bone cell. A normal cell activates just the genes it |
| which the bases occur determines the information | | | | needs at the moment and actively suppresses the |
| available, much as specific letters of the alphabet | | | | rest. Genes, through the proteins they encode, |
| combine to form words and sentences. | | | | determine all body processes, including how the body |
| DNA resides in the core, or nucleus, of each of the | | | | responds to challenges from the environment. |
| body's trillions of cells. Every human cell (with the | | | | |