Chromosome Walking

Chromosome WalkingPresented by: Erin A. Sharkawy

Chromosome WalkingChromosome walking is a method to move systematically along a chromosome from a known location.It is the only to search for a gene its position on a chromosome is only approximately known.The walking starts at the closest gene that has already been identified, known as a marker gene. Once the markers on either side of an unmapped sequence are found, the chromosome walk can begin from one of the markers. the probe is taken from the end of an insert which has a lesser chance of repetition.

Steps:1- the gene is fragmented into overlapped fragments by the restriction enzymes.2-the overlapped fragments are then inserted (cloned) into plasmids, phages or cosmids.3-the first insert (clone)is then isolated and sequenced.

4- a small segment of DNA from one end of the first recombinant (insert) is obtained and subcloned (cloned from a clone )and is then used as a probe to rescreen for the next insert of the genome containing this overlapping piece of DNA.5-the second insert is in turn sequenced and a terminal piece of it is subcloned and then used to rescreen for the next third DNA insert and so on .-the process is repeated so as to walk down the chromosome.

ApplicationThis technique can be used for the analysis of genetically transmitted diseases, to look for mutations.Chromosome Walking is usedin the discovery of single-nucleotide polymorphism of different organisms. when a gene is too large (>100 kb) to be sequenced in one piece.

DisadvantagesThere is alimitationtothe speed of chromosome walkingbecause of the small size of the fragments that are to be cloned. Another limitation is the difficulty of walking through therepeated sequencethat are scattered through the gene. If the markers were too far away, it simply was not a viable option. Additionally, chromosome walking could easily be stopped by unclonable sections of DNA. A solution to this problem was achieved with the advent of chromosome jumping (Marx, 1989), which allows the skipping of unclonable sections of DNA.

Referenceshttp://answers.google.com/answers/threadview/id/139820.htmlhttp://feedforbiotech.blogspot.com/2011/03/chromosome-walking.htmlhttp://dmohankumar.files.wordpress.com/2012/08/chromosome-walking.pdfhttps://www.google.com.pk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CCoQFjAA&url=http%3A%2F%2Flecturesug3.files.wordpress.com%2F2012%2F09%2Flecture-15.ppt&ei=lNBbUpScE-Kv4QTUsYHIBw&usg=AFQjCNH25Coi17nNd4IwD7sUCgKIP479WQ&sig2=KTMTKSwexvcC8PTx4ux3NA&bvm=bv.53899372,d.Ymshttp://nar.oxfordjournals.org/content/33/13/e122.full http://uk.answers.yahoo.com/question/index?qid=20070303020202AA6wM9Uhttp://wiki.answers.com/Q/Applications_of_chromosome_walking_and_jumping#ref1http://www.wisegeek.com/what-is-chromosome-walking.htmhttp://www.genevoguebiotech.com/2012/09/chromosome-walking.html