Large extended families have traditionally been the mother lode of genetic research. From them came a precious commodity: links between the presence of a disease and the errant genes responsible for it. When medical researcher Nancy Wexler, for instance, went looking for the genetic cause of Huntington's disease in 1979, it was a 9,000-member Venezuelan family that enabled her to trace the telltale patterns of disease inheritance.

Wayne Gulliver's family is not nearly so large, but it is impressive nonetheless. Until two years ago, when his great-great-aunt passed away, six generations of Gullivers were alive in Newfoundland. His grandmother, who died last October, had some hundred descendants, while his parents, only in their 60s, already have 26 grandchildren to go with their 10 children. All of this would be professionally irrelevant if Gulliver's family were not typical of Newfoundland, and if Gulliver himself, a dermatologist who studies the genetics of psoriasis, were not involved in a rapidly emerging discipline called population genomics, the goal of which is to identify the underlying genes responsible for common chronic diseases, such as cancer and heart disease.

Two years ago Gulliver met Paul Kelly, CEO of the British company Gemini Genomics, which had already assembled a huge international network of twins to use in searching for gene-disease associations. Gulliver pitched Kelly the idea of supplementing Gemini's database with population statistics from Newfoundland and Labrador. His selling points were simple: a population of 550,000, of which almost 90 percent are descended from the original Irish, Scottish and English immigrants who arrived before the mid-19th century. It is, Gulliver says, a population in which the locals often know their family lineages back to the original immigrants. "Not like the States," he says, "where you have three kids, send them off to college, and you might be lucky if you see each other every fifth Thanksgiving."

And many of those families, like Gulliver's own, are large. In such a tightly knit population consisting of large extended families, common diseases might run in recognizable patterns-shared by siblings, for instance, or passing through paternal or maternal lines, or linked to other distinctive physical characteristics. All it would take to mine this rich vein of medical history for valuable clues to disease-causing genes would be a sufficient effort, some very advanced biotechnology tools and some startup capital.