Sequences of Base Pairs Mapping
Illustration of the several conventions for mapping sequences of base pairs
on a chromosome.
- Genetic maps are representations of disease traits, physiological
traits, or random genes assigned to particular chromosomes and mapped relative
to one anothre. This model of a genetic map shows the location of 8 markers
(called here A-H) along the chromosome. The triangle maps a small part
of the chromosome in greater detail, as may be needed for an intensively
studied partion. Distances in genetic maps are measured in centimorgans
(cM, about 1 million base pairs).
- Physical maps are not representations but overlapping collections
of DNA fragments. DNA is snipped into fragments by the action of restriction
enzymes, then cloned and stored in a variety of forms such as plasmids in bacteria or YACs
in yeast. These tiny fragments (measured in kilobases, kb) may then
be analyzed by various means to discover the base-by-base sequence of DNA.