Chromosome Walking vs Chromosome Jumping
CHROMOSOME JUMPING
Chromosome jumping is a special type of chromosome walking that takes advantage of the breakpoints of chromosomal rearrangements as guide posts and permits the cloning of the two ends of a DNA sequence without the middle section. The procedure may take advantage of existing chromosomal rearrangements or the genomic DNA may be partially digested with any restriction endonuclease or with enzymes that cut very rarely. The DNA fragments are circularized with the aid of DNA ligase and cloned in such a way that the cloning vector contains a known E. coli sequence between the ligation sites. The cloned product is then digested by a restriction enzyme that does not cut within the special E. coli sequence. Thus the fragments generated contain the E. coli sequence flanked by the cloned target DNA sequence that was originally far away (100–150 kb) in the chromosome. The E. coli sequence containing fragments are then recloned in a phage vector and the DNA is probed to a DNA library to identify the clones that contain sequences far away in the eukaryotic genome. This procedure thus facilitates the rapid movement toward the genetic cloning target. It may also be combined with chromosome walking to approach the desired gene.
Advantages
Jumping of chromosome is the useful method for the cloning of the genes for responsible for human genetic disorders like cystic fibrosois. It is also used for the identification, isolation and cloning of the genes whose products are unknown and can’t be determined. Jumping on the chromosome has also been used to get the molecular marker and the gene of interest in close vicinity to each other so that the cloning of large fragments is avoided.
Key Difference – Chromosome Walking vs Jumping
Chromosome walking and chromosome jumping are two technical tools used in molecular biology for locating genes on the chromosomes and physical mapping of the genomes. Chromosome walking is a technique used to clone a target gene in a genomic library by repeated isolation and cloning of adjacent clones of the genomic library. Chromosomal jumping is a special version of chromosomal walking which overcomes the breakpoints of chromosomal walking. Chromosomal walking can only sequence and map small lengths of chromosomes while chromosomal jumping enables sequencing of large parts of chromosomes. This is the key difference between Chromosomal walking and chromosomal jumping.
What is Chromosome Walking?
Chromosome walking is a tool which explores the unknown sequence regions of chromosomes by using overlapping restriction fragments. In chromosome walking, a part of a known gene is used as a probe and continued with characterizing the full length of the chromosome to be mapped or sequenced. This goes from the marker to the target length. In chromosome walking, the ends of each overlapping fragments are used for hybridization to identify the next sequence. The probes are prepared from the end pieces of cloned DNA and they are subcloned. Then they are used to find the next overlapping fragment. All these overlapping sequences are used to construct the genetic map of the chromosome and locate the target genes. It is a method of analyzing long stretches of DNA by small overlapping fragments from the recontructed genomic library.
Chromosome Walking Technique – Steps
1. Isolation of a DNA fragment which contains the known gene or marker near target gene
2. Preparation of the restriction map of the selected fragment and subcloning the end region of the fragment to use as a probe
3. Hybridization of the probe with the next overlapping fragment
4. Preparation of the restriction map of the fragment 1 and subcloning of the end region of the fragment 1 to use as a probe for the identification of the next overlapping fragment.
5. Hybridization of the probe with the next overlapping fragment 2
6. Preparation of the restriction map of fragment 2 and subcloning of the end region of the fragment 2 to serve as a probe for the identification of the next overlapping fragment
What is Chromosome Jumping?
Chromosomal jumping is a technique used in molecular biology for physical mapping of genomes of the organisms. This technique was introduced to overcome a barrier of the chromosomal walking which arose upon finding the repetitive DNA regions during the cloning process. Therefore, chromosome jumping technique can be considered as a special version of chromosomal walking. It is a rapid method compared to chromosomal walking and enables bypassing of the repetitive DNA sequences which are not prone to be cloned during chromosomal walking. Chromosomal jumping narrows the gap between the target gene and the available known markers for genome mapping. Chromosome jumping tool starts with the cutting of a specific DNA with special restriction endonucleases and ligation of the fragments into circularized loops. Then a primer designed from a known sequence is used to sequence the circularized loops. This primer enables jumping and sequencing in an alternative manner. Hence, it can bypass the repetitive DNA sequences and rapidly walk through the chromosome for the search of the target gene. The discovery of the gene encodes for cystic fibrosis disease was done using the chromosomal jumping tool. Combined together, chromosomal jumping and walking can enhance the genome mapping process.
– Chromosome Walking vs Jumping
Chromosomal walking is frequently applied when it is known that a particular gene is located near a previously cloned gene in a chromosome and it is possible to identify it with repeated isolation of adjacent genomic clones from the genomic library. However, when repetitive DNA regions are found during the chromosomal walking technique, the process cannot be continued. Hence, the technique breaks from that point. Chromosomal jumping is a molecular biological tool which overcomes this limitation for mapping genomes. It bypasses these repetitive DNA regions which are difficult to clone and helps in physical mapping of genomes. This is the main difference between chromosome walking and jumping.