Gene mapping
[5] The genetic basis to gene maps is to provide an outline that can potentially help researchers carry out DNA sequencing.
These techniques consequently allow researchers to observe chromosomes directly so that a map may be constructed with relative gene positions.
These technique allow for maps to be constructed so that relative positions of genes and other important sequences can be analyzed.
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, for example 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.
[citation needed] In gene mapping, any sequence feature that can be faithfully distinguished from the two parents can be used as a genetic marker.
The entire process is then repeated by looking at more markers that target that region to map the gene neighborhood to a higher resolution until a specific causative locus can be identified.
[10] The great advantage of genetic mapping is that it can identify the relative position of genes based solely on their phenotypic effect.
[12] The basis to linkage analysis is understanding chromosomal location and identifying disease genes.
During meiosis, these genes are capable of being inherited together and can be used as a genetic marker to help identify the phenotype of diseases.
[13] The earliest gene maps were done by linkage analysis of fruitflies, in the research group around Thomas Hunt Morgan.
By analyzing the fingerprints, contigs are assembled by automated (FPC) or manual means (pathfinders) into overlapping DNA stretches.
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.
[16] Fluorescence in situ hybridization (FISH) is a method used to detect the presence (or absence) of a DNA sequence within a cell.
[17] DNA probes that are specific for chromosomal regions or genes of interest are labeled with fluorochromes.
By attaching fluorochromes to probes, researchers are able to visualize multiple DNA sequences simultaneously.
[6] A sequence-tagged site (STS) is a short sequence of DNA (about 100 - 500 base pairs in length) that is seen to appear multiple times within an individual's genome.
Sequenced tagged sites can be mapped within our genome and require a group of overlapping DNA fragments.
In order to calculate the map distance between STSs, researchers determine the frequency at which breaks between the two markers occur (see shotgun sequencing)[16] In the early 1950s the prevailing view was that the genes in a chromosome are discrete entities, indivisible by genetic recombination and arranged like beads on a string.
He found that, on the basis of recombination tests, the sites of mutation could be mapped in a linear order.
[18][19] This result provided evidence for the key idea that the gene has a linear structure equivalent to a length of DNA with many sites that can independently mutate.
Although not strictly additive, a systematic relationship was demonstrated[22] that likely reflects the underlying molecular mechanism of genetic recombination.
The process of shotgun sequencing[23] 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).
Researchers then had completed linkage analysis on additional DNA markers within chromosome 7 to identify an even more precise location of the CF gene.
