Figure 1

Distribution of rare causal SNPs within families. In the GAW17 data set, 145 of 162 casual SNPs are rare variants. Of these 145 rare variants, 103 do not exist in the family data. Eighty-five percent of the existing rare variants exist in only one or two families. The number above each bar indicates the exact number of rare SNPs in this category. It partly explains why many rare variants cannot be discovered using family data.