Also found in: Dictionary, Encyclopedia.
Etymology: L, mappa, napkin, unus, one
an arbitrary unit of measure used to express the distance between genes on a chromosome. It is calculated from the percentage of recombinations that occur between specific genes so that 1% of crossing over represents one unit on a genetic map, or approximately the number of new combinations that can be detected. The measurement is accurate only for small distances because double crossovers do not appear as new recombinations. Also called map distance. See also morgan.
map unitAn arbitrary unit for the distance between genes, usually derived from the percentage of recombination, but also defined by the time at which the gene is transferred during conjugation. One map unit corresponds to a recombination frequency of 1%.
linkage unita unit of ‘distance’ between genes along a chromosome. The number of map units is directly correlated with the amount of RECOMBINATION between loci; 1% recombination is equal to 1 map unit. See CROSS-OVER VALUE, GENETIC LINKAGE.
map distance, map unit
the amount of recombination between two genes expressed as a percentage. See also centimorgan.