geneticists hook up with a giant network of people to nail down the exact locations of genes:

1. Physicians identify a disorder by observing a phenotype caused by
mutation. Essentially, this is the face of the gene.
2. Genetic counselors work with patients and their families to gather complete
medical histories (see Chapter 12). Analysis of family trees may
uncover other traits that associate with the disorder.
3. Cell biologists look at the karyotypes of many affected people and link
traits to obvious chromosomal abnormalities. These large-scale changes
in chromosomes often provide hints about where genes reside. (Chapter
15 examines methods of karyotyping.)
4. Population geneticists analyze the DNA of large groups of people with
and without the disease to narrow down which chromosomes and which
genes are involved with the disease.
5. Biochemists study the chemical processes in the affected organs of
people with the disease to identify the physiology of the disorder. Often,
they’re able to nab the precise protein-gone-wrong.
6. With the protein in hand, geneticists use the genetic code (profiled in
Chapter 9) to work backwards from the building blocks of that protein,
the specific amino acids, to discern what the mRNA instructions were.