Distances between genes on chromosomes as estimated based upon frequencies of recombination.
The more closely linked two loci then the lower the frequencies with which the two loci are separated by recombination. Furthermore, the closer, physically, two genes are on a single chromosome then the more tightly linked those two genes are. One can use measures of frequency of recombination to estimate chromosomal distances among numerous loci, resulting in construction of gene order and gene distance maps that are called genetic or linkage maps.
Note the importance of performing crosses in generating genetic maps. As DNA sequencing technologies continue to improve, however, this process increasing is being replaced by whole or approximately whole genome sequencing.
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