How Your DNA Can Reconstruct Your Great-Great-Grandfather’s Genetic Code

21 May 2015

dna-kitMost people consider their children to be their legacy: people to pass on a mother’s trademark dimple, kids to carry on the family business, someone to tend the headstone. David Speegle, an Alabama farmer born more than 200 years ago, now has a distinctly 21st-century legacy, thanks to AncestryDNA.

By combining genetics and genealogy, Ancestry and AncestryDNA have been able to piece together a significant amount of the genetic code for Speegle and his two wives using only data from his descendants who have joined AncestryDNA.

In this breakthrough accomplishment, AncestryDNA was able to reconstruct Speegle’s genome without using any hair or other tissue samples from Speegle, who died in 1890. Instead, Ancestry relied on the technology behind its DNA Circles program, in which members send in samples of their saliva to learn more about their own genetic background and discover whether they’re related to other AncestryDNA members.

AncestryDNA combed through 500,000 genomic samples in their database to locate members with long, identical segments of DNA. They then traced each pair to a shared ancestor: Speegle, who was born in 1806. The fact that Speegle had 26 children with two wives and more than 150 grandchildren explains how he became the forefather to so many people today.

A professional genealogist examined the family trees of those members to confirm that they all shared Speegle as an ancestor. Then, relying on genetics and computer science, AncestryDNA used two processes to rebuild as much of the DNA for Speegle and his wives as possible.

First, AncestryDNA developed an in-house approach to stitch together all segments of DNA shared by any pair of individuals in the Speegle DNA circle. Since Speegle was the earliest common ancestor of those members, the geneticists knew those stretches must have come from Speegle and one of his wives — either Winifred, his first, or Nancy, whom he married after Winifred’s death. Then, relying on a technique used in livestock genetics, geneticists took a look at Speegle’s entire family tree and mapped how parts of the genome were transmitted upward through the pedigree back to Speegle and his wives.

With those two techniques, AncestryDNA was able to construct at least one copy of DNA for Speegle or his wives at 50 percent of all positions in the genome. AncestryDNA now knows certain aspects of Speegle and his wives’ genetic makeup. Speegle or his wives, for example, possessed the gene for blue eyes. At least one of them also carried a version of the gene known to cause male pattern baldness.

While validating the science behind DNA Circles, AncestryDNA’s use of descendants to reconstruct an ancestor’s DNA has broader applications. DNA technology, involving genome reconstruction or other methods, can fill in gaps in family lineages where historical records fall short.

“This is a significant achievement that will have implications in population genetics, genealogy, anthropology and health and offers a preview into future advancements that will be made possible by large databases of genetic and genealogical information,” said Dr. Kenneth Chahine, Senior Vice President and General Manager of AncestryDNA.

“It feels like science fiction, but it is very much a reality and only the beginning. Future insights may come in the form of tracing the source of particular traits in a population, reaching a better understanding of recent population history and enabling more targeted genetic genealogy research.”

While AncestryDNA might not help reconstruct the DNA of your great-great-great-grandfather, there are plenty of other insights the test has to offer, from your personal ethnicity estimate to dozens of living genetic cousins, all to help you come to know more about your past and yourself.

Sandie Angulo Chen