Genome Maps

A genome map is a linear representation of
genomic landmarks (genes and markers). It refers
either to a chromosome (cytogenetic map)
or to a stretch of DNA. A map provides knowledge
of the position of a particular genomic
landmark and its relation to others. Unraveling
the human genome in some respect resembles
the mapping of new continents five hundred
years ago.
A genetic map expresses the positions of genes
relative to each other without a physical anchor
on the chromosome. This is the type of map that
was first used by A. H. Sturtevant in 1913 when
working with T. M. Morgan (who started studying
Drosophila in 1910). Here, the distance between
markers is determined by the frequency
of recombination during meiosis, which is in
turn determined by the relative distance between
the loci (see p. 116). A physical map provides
knowledge of the exact position of a gene
or marker. Its distance to another locus on the
same chromosome is expressed by number of
base pairs (bp), a physical equivalent. A variety
of methods are employed to arrive at a physical
map.