Genetic Genealogy in the Genomic Era

Genealogy is the study of family history, which involves tracing one’s family lineages back through time. The idea of applying molecular genetics methods to genealogical research emerged in the 1990s and its use has dramatically expanded in the last decade thanks to a precipitous drop in the cost of genetic testing, which has enabled numerous companies to begin offering affordable genetic genealogy testing to the general public. This chapter introduces different testing options available that focus on different parts of the human genome and discuss the relative merits of each type. It then describes the underlying inheritance patterns for Y, mitochondrial, and autosomal DNA, and how these patterns determine what can be inferred about historical origins from each test type. In general haploid tests provide a deeper look into the past, but with results that are only relevant to one family lineage. On the other hand, while autosomal tests trace all genetic lineages, the semi-conservative nature of autosomal inheritance implies a much shallower look into the past. Finally, we touch upon what these tests can tell us about living relatives by looking for long contiguous blocks of DNA shared between two or more test-takers due to a shared ancestor. These are said to be “identical by descent” or IBD blocks. The explosive growth of the human population in recent generations implies tremendous amounts of IBD sharing, and this network of sharing, as revealed in vast direct-to-consumer databases, is quickly becoming an appealing and powerful forensic tool.