Fig. 1 Pedigrees used in timing experiments. Filled symbols represent affected individuals and genotypes are unavailable for individua ls represented by symbols with a slash. a, Pedigree p1, containing a simple marriage loop. b, Pedigree p4, which is approximately the largest pedigree that can be analysed with Allegro on a computer with one gigabyte of memory. Pedigree p3 is obtained from pedigree p4 by removing the seventh, eighth and eleventh individuals in the third generation, and pedigree p2 is obtained by further removing the remaining unaffected sister in the third generation and the unaffected brothers in the fourth generation.