Gene identification

Once the chromosomal location of a gene has been identified,
there are several strategies that can be employed to isolate the
gene itself. Genes within the region of interest can be searched
for by using techniques such as cDNA selection and screening,
CpG island identification and exon trapping. Any genes
identified can then be studied for mutations in affected
individuals. Alternatively, candidate genes can be identified by
their function or expression patterns or by sequence homology
with genes known to cause similar phenotypes in animals. The
gene for Waardenburg syndrome, for example, was localised to
chromosome 2q by linkage studies and the finding of a
chromosomal abnormality in an affected subject. Identification
of the gene was then aided by recognition of a similar
phenotype in splotch mice. Mutations in the PAX3 gene were
found to underlie the phenotype in both mice and humans.