Chromosome mapping is the assignment of genes to specific locations on a chromosome. A gene map serves many important functions and is much like understanding the basic human anatomy to allow doctors to diagnose patients with disease. A doctor requires knowledge of where each organ is located as well as the function of this organ to understand disease. A map of the human genome will allow scientist to understand where genes are located so that its function within the human genome can be elucidated. A detailed chromosome map also provides methods to study how genes are segregated and how genetic heterogeneity (variation between a particular gene maternally inherited and the same gene with a slightly different sequence that is paternally inherited) can help identify disease genes. Gene mapping can provide clinicians with useful information regarding genes that are linked, or segregate closely together.
Scientists use several methods to map genes to the appropriate locations. These methods include family studies, somatic cell genetic methods, cytogenetic techniques, and gene dosage studies. Family studies are used to determine whether two different genes are linked close together on a chromosome. If these genes are linked, it means they are close together on the same chromosome. Additionally, the frequency with which the genes are linked is determined by recombination events (crossing over of the chromosomes during meiosis) between known locations or markers, and determines the linear order or genetic distance. In somatic cell genetic methods, chromosomes are lost from a special type of cell and the remaining chromosome that has one gene, but not a different gene, would suggest that they are located on different chromosomes. This method allows scientists to identify which chromosome contains the gene, and represents one of the first mapping methods used by scientists.