Historical inferences from genetic data increasingly depend on assumptions about the genealogical process that shapes the frequencies of alleles over time. Yet little is known about the structure of human genealogies over long periods of time and how they depart from expectations of standard demographic models, such as that attributed to Wright and Fisher. To obtain such information and to examine the recent evolutionary history of mtDNA and Y-chromosome haplotypes in the Icelandic gene pool, we traced the matrilineal and patrilineal ancestry of all 131,060 Icelanders born after 1972 back to two cohorts of ancestors, one born between 1848 and 1892 and the other between 1798 and 1742. This populationwide coalescent analysis of Icelandic genealogies revealed highly positively skewed distributions of descendants to ancestors, with the vast majority of potential ancestors contributing one or no descendants and a minority of ancestors contributing large numbers of descendants. The expansion and loss of matrilines and patrilines has caused considerable fluctuation in the frequencies of mtDNA and Y-chromosome haplotypes, despite a rapid population expansion in Iceland during the past 300 years. Contrary to a widespread assumption, the rate of evolution caused by this lineage-sorting process was markedly faster in matrilines (mtDNA) than in patrilines (Y chromosomes). The primary cause is a 10% shorter matrilineal generation interval. Variance in the number of offspring produced within each generation was not an important differentiating factor. We observed an intergenerational correlation in offspring number and in the length of generation intervals in the matrilineal and patrilineal genealogies, which was stronger in matrilines and thus contributes to their faster evolutionary rate. These findings may have implications for coalescent date estimates based on mtDNA and Y chromosomes.
populationwide
Methods and results: This cost-effectiveness analysis was made from data from the literature and the Coronary Heart Disease Policy Model and was based on the US population age 35 to 84 years. Study interventions were populationwide programs to reduce serum cholesterol levels with costs and cholesterol-lowering effects similar to those reported from the Stanford Three-Community Study, the Stanford Five-City Project, and in North Karelia, Finland. The main outcome measures were cost-effectiveness ratios, defined as the change in projected cost divided by the change in projected life-years when the population receives the intervention compared with the population without the intervention. A populationwide program with the costs ($4.95 per person per year) and cholesterol-lowering effects (an average 2% reduction in serum cholesterol levels) of the Stanford Five-City Project would prolong life at an estimated cost of only $3200 per year of life saved. Under a wide variety of assumptions, a populationwide program would achieve health benefits at a cost equivalent to that of many currently accepted medical interventions. Such programs would also lengthen life and save resources under many scenarios, especially if the program affected persons with preexisting heart disease or altered other coronary risk factors. 2ff7e9595c
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