In order to determine the genes that may be involved, scientists also perform what are referred to as "genome screens." To do this they use maps of the chromosomes (similar to road maps) in order to look for genes. Just as gas stations or restaurants can be used as landmarks when locating a friend's house, scientists use markers to find a gene. Markers are known regions or "sequences" of DNA along the chromosomes that may differ slightly from person to person or among populations. These differences, or "polymorphisms," serve as landmarks that can be tested in individuals. In performing a genome screen, researchers look at many different markers throughout the genome, trying to find markers that are consistently found in family members who have a particular disorder, but not in family members without the disorder. These markers are landmarks that identify which chromosome a gene is located on (similar to which street a house is on). Statistical methods can tell a scientist how close these markers are to a gene. Testing additional markers will narrow the search area of the gene (similar to which block a friend's house is on). Markers that are very close to a gene are said to be "linked" to that gene because the marker and the gene are almost always inherited together. Once scientists find a set of markers that are linked to a gene, then they say that they have found linkage. It is important to remember that linkage does not mean that a gene has been identified, but rather that the gene being searched for is somewhere nearby. There have been several published genome screens to date, and there are additional unpublished screens. Chromosomal regions of interest identified thus far include 2p, 4p, 6q, 7q, 9q, 13q, 15q, 19p, and Xq. Additional study will be needed to confirm linkage in these regions, and to narrow down the areas further.

• Candidate Genes
• Exploring Chromosome 2
• Exploring Chromosome 3
• Exploring Chromosome 7
• Exploring Chromosome 15
• Searching Chromosome X

HOW GENES ARE NAMED
You may wonder how genes are named. As you may have guessed, some names are abbreviations for the full gene names. Other genes are named after similar genes in other organisms. More ...

WHAT IS A CHROMOSOME?
Chromosomes are structures that contain genes. Chromosomes are visible with a microscope and are located in the nucleus of a cell. Almost every human chromosome contains thousands of individuals genes. More ...

HOW CHROMOSOME ABNORMALITIES HELP US FIND GENES
Genetic researchers use many different tools and strategies to look at the genetic material (DNA) inside our cells to find the exact gene(s) that cause a genetic disorder such as autism. More ...