New estimates of intergenerational time intervals for the calculation of age and origins of mutations

Intergenerational time intervals are frequently used in human population-ge netics studies concerned with the ages and origins of mutations. In most ca ses, mean intervals of 20 or 25 years are used, regardless of the demograph ic characteristics of the population under study. Although these characteri stics may vary from prehistoric to historical times, we suggest that this v alue is probably too low and that the ages of some mutations may have been underestimated. Analyses were performed by using the BALSAC Population Regi ster (Quebec, Canada), from which several intergenerational comparisons can be made. Family reconstitutions were used to measure interval lengths and variations in descending lineages. Various parameters were considered, such as spouse age at marriage, parental age, and reproduction levels. Mother-c hild and father-child intervals were compared. Intergenerational male and f emale intervals were also analyzed in 100 extended ascending genealogies. R esults showed that a mean value of 30 years is a better estimate of interge nerational intervals than 20 or 25 years. As marked differences between mal e and female interval length were observed, specific values are proposed fo r mtDNA, autosomal, X-chromosomal, and Y-chromosomal loci. The applicabilit y of these results for age estimates of mutations is discussed.