Chromosome walking is a method used to isolate and clone a specific allele in a gene library. It involves starting from a known marker gene and testing each successive gene in the sequence until the mutant gene is found. This process is complex and time-consuming, and requires well-equipped laboratories.
Chromosome walking is a positional cloning method used to find, isolate and clone a particular allele in a gene library. An allele is a gene for a particular genetic trait passed from adults to their offspring, such as the allele for brown eyes in a gene for eye color. Sometimes, the approximate position of a single allele in a string of deoxyribonucleic acid (DNA) may be known. To isolate a particular allele for a genetically transmitted disease, it may be necessary to walk the chromosome walking to locate the desired sample in an unmapped DNA sequence outside the previously mapped sequences.
To locate a particular disease gene, the path starts from the closest gene that has already been identified, known as a marker gene. Each successive gene in the sequence is tested repeatedly for so-called overlap restrictions and mapped for their precise position in the sequence. Eventually, walking through the genes leads to the mutant gene in an unmapped sequence that binds to a fragment of a gene from that particular disease. Once the gene has been cloned, its function can be fully identified. During this process, tests are performed to fully identify the properties of each successive clone, to map their locations for future use.
There are nearly half a dozen positional cloning tests that are performed prior to a chromosome walk, to narrow down as much as possible the particular genetic sequences that may contain the desired mutant gene for a disease. Once markers are found on either side of an unmapped probable sequence, the chromosome pathway can start from one of the markers. Testing each successive clone is complex, time-consuming, and varies by species. There are several tests for genes related to plant diseases versus genes involved in a human genetic library.
Positional cloning uses genetic markers known to inhabit the chromosomes of individuals who have specific diseases. These databases of known common traits allow for tests that can be used to identify individuals who may or may not have certain recessive genes for a disease that hasn’t shown up yet. Chromosome walking, along with all other tests performed prior to chromosome walking, requires exceptionally well-equipped laboratories in which all cloning steps, testing and mutation analysis can be performed.
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