Agriculture Reference
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same chromosome. The degree to which the two characteristics are inherited
together, in other words the strength of the linkage, can be quantified.
Characteristics that rarely recombine can be assumed to be controlled by genes
that are very close to each other along the same chromosome, so that their alleles
are rarely resorted by crossing over during meiosis.
By quantifying the frequencies of recombination between linked gene loci
for a number of characteristics it is possible to order the strength of the linkages
between them and construct a 'linkage map' showing their relative positions
along the chromosome (see Fig. 3.4). The chromosomes are the physical reality
Fig. 3.4.
Genetic maps of alliums. (a) A linkage map of
A. cepa
(shallot)
chromosome 4. The long codenames apply to DNA markers of the Amplified
Fragment Length Polymorphism (AFLP) type that was used for map construction.
The locations of the genes coding for the enzymes alliinase, malate dehydrogenase
(MDH) and phosphoglucomutase (PGM) are shown on the map (part of Fig. 2 of
