r. (fig 2.2).The shotgun approach is therefore inappropriate for the Human genome. Instead, it was agreed that a genome map must be first generated. This would provide a guide for the sequencing experiments by showing the positions of genes and other distinctive features. For these reasons, the first 6 years of the human genome project were devoted almost exclusively to mapping the human genome, rather than sequencing it.The convention has been to divide genome mapping methods into two categories. The first, and the older of the two techniques is genetic mapping. This technique is based on the use of genetic techniques to construct maps showing the positions of genes and other sequence features on a genome. The second type of mapping, is physical mapping, which uses molecular biology to examine DNA molecules directly in order to construct maps showing the positions of sequence features including genes.As with any type of map, a genetic map must show the positions of distinctive features. In a geographical map these markers are recognisable components of the landscape, such as rivers, roads, and buildings. What markers however could be used in a genetic landscape?The first comprehensive human genetic map was published only in 1987, but within 7 years very high resolution maps were achieved, mostly using microsatallite markers. Using classical methods of genetic mapping, meant that human genetic maps could not feasibly be achieved. Classical genetic maps for experimental organisms such as Drosophilia and mouse are based on genes. They have been available for decades, and have been refined continuously. They are constructed by crossing different mutants in order to determine whether the two gene loci are linked or not. For much of this period, human geneticists were envious spectators, given that a human genetic map was unattainable. Unlike the experimental organisms, the human genetic map was never going to be based on genes because of th...
