Gene mapping is the sequential allocation of loci to a relative position on a chromosome. Genetic maps are species-specific and comprised of genomic markers and/or genes and the genetic distance between each marker. These distances are calculated based on the frequency of chromosome crossovers occurring during meiosis, and not on their physical location on the chromosome. There are existing dense genetic marker maps available for humans, and the introduction of next-generation sequencing technologies is facilitating increased construction of genetic maps for other species. Genetic maps are a necessary tool for mapping of disease genes or trait loci, a method also commonly known as linkage mapping. Integrating genetic mapping and disease gene mapping with next-generation sequencing has proven to be a powerful strategy in genetic research.