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We can see if two genes are linked, and how tightly, by using data from genetic crosses to calculate the recombination frequency. By finding recombination frequencies for many gene pairs, we can make linkage maps that show the order and relative distances of the genes on the chromosome.
Gene mapping or genome mapping describes the methods used to identify the location of a gene on a chromosome and the distances between genes. [2] [3] Gene mapping can also describe the distances between different sites within a gene.
In Sturtevant's gene map, six traits are arranged along a linear chromosome according to the relative distance of each from trait B. Traits include yellow body (B), white eyes (C, O),...
A genetic map shows the map distance, in cM, that separates any two loci, and the position of these loci relative to all other mapped loci. The genetic map distance is roughly proportional to the physical distance, i.e., the amount of DNA between two loci.
Genetic maps provide an outline for the location of genes within a genome, and they estimate the distance between genes and genetic markers on the basis of recombination frequencies during meiosis.
Comparisons between genetic maps and the actual positions of genes on DNA molecules, as revealed by physical mapping and DNA sequencing, have shown that some regions of chromosomes, called recombination hotspots, are more likely to be involved in crossovers than others.
Physical maps specify the distances between landmarks along a chromosome. Ideally, the distances are measured in nucleotides, so that the map provides a direct description of a chromosomal DNA molecule. The most important landmarks in physical mapping are the cleavage sites of restriction enzymes.
