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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.
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. Gene mapping can also describe the distances between different sites within a gene. The essence of all genome mapping is to place a collection of molecular markers onto their respective positions on the ...
The genetic map distance is roughly proportional to the physical distance, i.e., the amount of DNA between two loci. For example, in Arabidopsis , 1.0 cM corresponds to approximately 150,000 bp and contains approximately 50 genes.
Human genome maps are constructed on several different scales or levels of resolution. At the coarsest resolution are genetic linkage maps, which depict the relative chromosomal locations of DNA markers (genes and other identifiable DNA sequences) by their patterns of inheritance.
Since there are 24 different DNA molecules in the human genome, a complete human gene map consists of 24 maps, each in the linear form of the DNA molecule itself. One type of useful genome map is the messenger RNA (mRNA) or exon map.
A physical map is a representation of the physical distance, in nucleotides, between genes or genetic markers. Both genetic linkage maps and physical maps are required to build a complete picture of the genome.
