Gene
Mapping
Gene mapping is a technique used to find the precise location of genes on chromosomes.
By testing large families, the chromosomal location of genes for many traits, including several forms of deafness, has been determined. The demonstration that deafness can result from changed genes at many different chromosomal locations proves the existence of genetic heterogeneity.
Using these techniques, it has been possible to show that changed genes located at five different sites can give rise to Usher syndrome, and genes located at two or more sites can give rise to Waardenburg syndrome. Similarly, at least 22 different forms of dominant and recessive non-syndromic deafness have been mapped to different chromosomal regions.
Several different strategies can be used to map genes for deafness.
In the most common strategy, the inheritance of two traits within a family
are compared. The chromosomal location of one trait (deafness) is
unknown. The chromosomal location of the second trait (a
genetic marker)
is known. To map a gene for deafness, a researcher tests one marker
after another until one is found that is always inherited with the gene
for deafness. If such a genetic marker is found, the gene for deafness
must be near the known location of the genetic marker.
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page—Molecular Characterization of Genetic Deafness