cystic fibrosis (CF)

Positional cloning of the gene for

The CFTR gene was isolated on the basis of its
chromosomal location (positional cloning) on
the long arm of chromosome 7 at q31 (7q31).
Since the gene could be mapped to the long arm
of chromosome 7 near a marker locus D7S15, a
long-range restriction map comprising about
1500 kb containing the presumptive CF locus
flanked by two marker loci, MET and D7S8, was
constructed. From there a region of 250 kb was
isolated by a combination of chromosome
walking and chromosome jumping. Several
genes were located in this region (candidate
genes) between the marker loci D7S340 and
D7S424. The gene sought was identified by the
finding of mutations of this gene in patients but
not in controls, by comparing with similar
genes in other organisms (evolutionary conservation),
by determining its exon/intron structure,
by sequencing it, and by determining the
expression pattern of the gene in different tissues.