Chromosome walking

Chromosome walking is a method in genetics for identifying and sequencing long parts of a DNA strand, e.g., a chromosome. As long DNA strands cannot be sequenced, this method works by dividing the long sequence into several short ones. Basically, chromosome walking works as follows:

1. A primer that matches the beginning of the DNA to sequence is used to synthesize a short DNA strand complementary to the unknown sequence, starting with the primer (see PCR).
2. The new short DNA strand is sequenced.
3. The end of the sequenced strand is used as a primer for the next part of the long DNA sequence.

That way, the short part of the long DNA that is sequenced keeps "walking" along the sequence. The method can be used to sequence entire chromosomes (thus, chromosome walking). A different method with the same purpose which becomes more popular for large-scale sequencing (e.g., the Human Genome Project) is shotgun sequencing.