Gene localisation

Prior to 1980, only a few genes, for disorders whose
biochemical basis was known, had been identified. With the
advent of molecular techniques the first step in isolating many
genes for human diseases was to locate their chromosomal
position by gene mapping studies. In some disorders, such as
Huntington disease, this was achieved by undertaking linkage
studies using polymorphic DNA markers in affected families,
without any prior information about which chromosome
carried the gene. In other disorders, the likely position of the
gene was suggested by identification of a chromosomal
rearrangement in an affected individual in whom it was likely
that one of the chromosomal break points disrupted the gene.
The neurofibromatosis type 1 (NF1) gene, for example, was
isolated after the identification of such a translocation followed
by cloning and sequencing of DNA from the region of the
break point on chromosome 17.