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.
* 2 Use of gene mapping
* 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.
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 don't. Scientists then isolate
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.
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
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
There are alternative ways to determine how
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.
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.
* ^ Mader, Sylvia (2007). Biology Ninth Edition. New York:
McGraw-Hill. p. 209. ISBN 978-0-07-325839-3 .
* ^ "
* Brown, Terry A. (2007). Genomes 3. New York, NY: Garland Science
Publishing . ISBN 9780815341383 .