A study of contemporary levels and temporal trends in inbreeding in the Tangier Island, Virginia, population using pedigree data and isonymy

• Published in: American journal of physical anthropology Vol. 112; no. 1; pp. 29 - 38
• Main Authors: Mathias, Rasika A., Bickel, Carol A., Beaty, Terri H., Petersen, Gloria M., Hetmanski, Jacqueline B., Liang, Kung-Yee, Barnes, Kathleen C.
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01-05-2000; Wiley-Liss
• Subjects: Adolescent; Adult; Aged; Anthropology. Demography; Biological and medical sciences; Child; Child, Preschool; Consanguinity; Emigration and Immigration; Female; Genetics, Population; Human physiology applied to population studies and life conditions. Human ecophysiology; Humans; inbreeding; Infant; Infant, Newborn; isolate; isonymy method; Male; Medical sciences; Middle Aged; Names; Pedigree; pedigree method; Virginia; United States; North America; Virginia; America; Human; Isonymy; Pedigree selection; Anthropology; Inbreeding coefficient; Methodology
• ISSN: 0002-9483; 1096-8644
• DOI: 10.1002/(SICI)1096-8644(200005)112:1<29::AID-AJPA4>3.0.CO;2-5

In this study we describe inbreeding in a large pedigree from Tangier Island, Virginia, in which we compare two commonly used methods to estimate inbreeding in humans: pedigree and isonymy (identical surnames of spouses). Genealogical data on 3,512 individuals dating back to 1722 were used. Using the pedigree method, we determined an average inbreeding coefficient (F) of 0.00873 for the community as a whole, and 0.018 for inbred individuals. Analysis of temporal trends showed that inbreeding began around 1800 and peaked at 0.0109 in 1824–1849 and 1875–1899. Thereafter, inbreeding steadily declined to 0.00565 in 1975–1997. Analysis of pedigree structure complexity over time showed that close consanguinity contributes to inbreeding in the earlier cohorts, and remote consanguinity accounts for much of the inbreeding in the later cohorts. The number of common ancestors increases over time, as does the number of paths connecting inbred individuals to these common ancestors. Inbreeding estimates based on the isonymy approach yielded a 2.2‐fold higher value of F (0.01945) compared to the pedigree method. Total isonymy estimates over 25‐year cohorts overestimated inbreeding values from pedigree data between 1.5–8‐fold. We speculate that the overestimation is probably due to the inability of our data to satisfy the method's assumption of monophyletic origin of each surname. In conclusion, inbreeding in the Tangier Island population is consistent with the isolated nature of its population, and temporal trends reflect patterns in emigration and a breakdown in isolation over time. Am J Phys Anthropol 112:29–38, 2000. © 2000 Wiley‐Liss, Inc.