Gene mapping describes the methods which used to identify the locus of a gene and the distances between genes. Gene mapping can also describe the distances between different sites within a gene. The essence of all genome mapping is to place a collection of molecular markers onto their respective positions on the genome. There are two types of gene mapping: Genetic Mapping - using linkage analysis to determine the relative position between two genes on a chromosome. Physical Mapping - using all available techniques or information to determine the absolute position of a gene on a chromosome