Gene mapping - wikipedia Gene mapping This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( September 2013 ) Thomas Hunt Morgan 's Drosophila melanogaster genetic linkage map. This was the first successful gene mapping work and provides important evidence for the Boveri -- Sutton chromosome theory of inheritance. The map shows the relative positions of allelic characteristics on the second Drosophila chromosome. The distance between the genes ( map units ) are equal to the percentage of crossing - over events that occurs between different alleles. Gene mapping describes the methods used to identify the locus of a gene and the distances between genes. The essence of all genome mapping is to place a collection of molecular markers onto their respective positions on the genome. Molecular markers come in all forms. Genes can be viewed as one special type of genetic markers in the construction of genome maps, and mapped the same way as any other markers. Contents 1 Gene mapping vs. physical mapping 1.1 Gene mapping 1.2 Physical mapping 1.3 Genome sequencing 2 Use of gene mapping 2.1 Disease association 3 See also 4 References 5 External links Gene mapping vs physical mapping There are two distinctive types of `` Maps '' used in the field of genome mapping : genetic maps and physical maps. While both maps are a collection of genetic markers and gene loci, genetic maps ' distances are based on the genetic linkage information, while physical maps use actual physical distances usually measured in number of base pairs. While the physical map could be a more `` accurate '' representation of the genome, genetic maps often offer insights into the nature of different regions of the chromosome, e.g. the genetic distance to physical distance ratio varies greatly at different genomic regions which reflects different recombination rates, and such rate is often indicative of euchromatic ( usually gene - rich ) vs heterochromatic ( usually gene poor ) regions of the genome. Gene mapping Researchers begin a genetic map by collecting samples of blood or tissue from family members that carry a prominent disease or trait and family members that do n't. Scientists then isolate DNA from the samples and closely examine it, looking for unique patterns in the DNA of the family members who do carry the disease that the DNA of those who do n't carry the disease do n't have. These unique molecular patterns in the DNA are referred to as polymorphisms, or markers. The first steps of building a genetic map are the development of genetic markers and a mapping population. The closer two markers are on the chromosome, the more likely they are to be passed on to the next generation together. Therefore, the `` co-segregation '' patterns of all markers can be used to reconstruct their order. With this in mind, the genotypes of each genetic marker are recorded for both parents and each individual in the following generations. The quality of the genetic maps is largely dependent upon these factors : the number of genetic markers on the map and the size of the mapping population. The two factors are interlinked, as a larger mapping population could increase the `` resolution '' of the map and prevent the map being `` saturated ''. In gene mapping, any sequence feature that can be faithfully distinguished from the two parents can be used as a genetic marker. Genes, in this regard, are represented by `` traits '' that can be faithfully distinguished between two parents. Their linkage with other genetic markers are calculated same way as if they are common markers and the actual gene loci are then bracketed in a region between the two nearest neighbouring markers. The entire process is then repeated by looking at more markers which target that region to map the gene neighbourhood to a higher resolution until a specific causative locus can be identified. This process is often referred to as `` positional cloning '', and it is used extensively in the study of plant species. Physical mapping Since actual base - pair distances are generally hard or impossible to directly measure, physical maps are actually constructed by first shattering the genome into hierarchically smaller pieces. By characterizing each single piece and assembling back together, the overlapping path or `` tiling path '' of these small fragments would allow researchers to infer physical distances between genomic features. The fragmentation of the genome can be achieved by restriction enzyme cutting or by physically shattering the genome by processes like sonication. Once cut, the DNA fragments are separated by electrophoresis. The resulting pattern of DNA migration ( i.e. its genetic fingerprint ) is used to identify what stretch of DNA is in the clone. By analyzing the fingerprints, contigs are assembled by automated ( FPC ) or manual means ( pathfinders ) into overlapping DNA stretches. Now a good choice of clones can be made to efficiently sequence the clones to determine the DNA sequence of the organism under study. In physical mapping, there are no direct ways of marking up a specific gene since the mapping does not include any information that concerns traits and functions. Genetic markers can be linked to a physical map by processes like in situ hybridization. By this approach, physical map contigs can be `` anchored '' onto a genetic map. The clones used in the physical map contigs can then be sequenced on a local scale to help new genetic marker design and identification of the causative loci. Macrorestriction is a type of physical mapping wherein the high molecular weight DNA is digested with a restriction enzyme having a low number of restriction sites. There are alternative ways to determine how DNA in a group of clones overlaps without completely sequencing the clones. Once the map is determined, the clones can be used as a resource to efficiently contain large stretches of the genome. This type of mapping is more accurate than genetic maps. Genome sequencing Genome sequencing is sometimes mistakenly referred to as `` genome mapping '' by non-biologists. The process of `` shotgun sequencing '' resembles the process of physical mapping : it shatters the genome into small fragments, characterizes each fragment, then puts them back together ( more recent sequencing technologies are drastically different ). While the scope, purpose and process are totally different, a genome assembly can be viewed as the `` ultimate '' form of physical map, in that it provides in a much better way all the information that a traditional physical map can offer. Use of gene mapping Identification of genes is usually the first step in understanding a genome of a species ; mapping of the gene is usually the first step of identification of the gene. Gene mapping is usually the starting point of many important downstream studies. Disease association The process to identify a genetic element that is responsible for a disease is also referred to as `` mapping ''. If the locus in which the search is performed is already considerably constrained, the search is called the fine mapping of a gene. This information is derived from the investigation of disease manifestations in large families ( genetic linkage ) or from populations - based genetic association studies. See also Genome project Human Genome Project Quantitative trait locus Genetic fingerprinting Genetic linkage Sulston score Optical mapping References Jump up ^ Mader, Sylvia ( 2007 ). Biology Ninth Edition. New York : McGraw - Hill. p. 209. ISBN 978 - 0 - 07 - 325839 - 3. Jump up ^ `` Gene mapping - Glossary Entry ''. Genetics Home Reference. Bethesda, MD : Lister Hill National Center for Biomedical Communications, an Intramural Research Division of the U.S. National Library of Medicine. 2013 - 09 - 03. Retrieved 2013 - 09 - 06. External link in work = ( help ) Jump up ^ https://www.genome.gov/10000715 Brown, Terry A. ( 2007 ). Genomes 3. New York, NY : Garland Science Publishing. ISBN 9780815341383. OCLC 444522997. External links `` Genetic Mapping Fact Sheet ''. Bethesda, MD : National Human Genome Research Institute, National Institutes of Health. Retrieved 2013 - 09 - 06. `` Canada 's Michael Smith Genome Sciences Centre ''. Vancouver, British Columbia. Retrieved 2013 - 09 - 06. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Gene_mapping&oldid=803463378 '' Categories : Genetics Hidden categories : CS1 errors : external links Articles needing additional references from September 2013 All articles needing additional references Talk Contents About Wikipedia Bosanski Deutsch Español فارسی Français Hrvatski Bahasa Indonesia Italiano Magyar Polski Português Русский Suomi Türkçe Українська 中文 Edit links This page was last edited on 2 October 2017, at 18 : 08. About Wikipedia

Question: physical location of a gene on a chromosome is called
Answer: locus