FIG. 1.

The disease-hitchhiking hypothesis. A new advantageous mutation arises on a chromosome with a rare disease-causing mutation. As the advantageous mutation (red dot) spreads rapidly through the population, the disease-causing mutation (red X) hitchhikes to relatively high frequency, and additional disease-causing mutations (green and blue Xs) are introduced into the sweeping haplotype block by recombination. Neutral and advantageous mutations are shown as dots, and disease-causing mutations are shown as crosses.