Fig. 9. Physical Mapping Strategies.

Top-down physical mapping (a) produces maps with few gaps, but map resolution may not allow location of specific genes. Bottom- up strategies (b) generate extremely detailed maps of small areas but leave many gaps. A combination of both approaches is being used. [Source: Adapted from P. R. Billings et al., New Techniques for Physical Mapping of the Human Genome, The FASEB Journal 5(1), 29 (1991).]