Scientists Study Doppelgängers to Find Genomic Link

unrelated look-alikes share more common genetic sequences than most people

By Jonny Lupsha, Wondrium Staff Writer

A photography project of similar-looking people has interested scientists. So-called “doppelgängers” bear an uncanny resemblance to each other despite no relation. Comparable epigenomes could hold the key.

Blue DNA helix on dark background
DNA testing of doppelgängers shows that the two people share very similar genomes, although the people are not related within a family. Photo by Olesya Kuznetsova

Most of us have mistaken a stranger for someone we know. However, sometimes it goes a step farther: Every so often, two completely unrelated people look similar enough that it causes confusion even among close friends or family. This is the doppelgänger phenomenon.

Public interest in doppelgängers has recently spiked on social media—and among some geneticists—thanks to Canadian artist François Brunelle’s photography project, I’m Not a Look-Alike! Brunelle’s project has captured so many of these incidents that researchers recruited 32 pairs of people from the project for DNA tests. They found that although unrelated by family, these doppelgängers shared very similar genomes compared to most other people.

Mapping the human genome was a massive endeavor. In his video series Understanding Genetics: DNA, Genes, and Their Real-World Applications, Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center in Duarte, CA, recalls how it came to pass.

The Earlier Days of Genetic Research

According to Dr. Sadava, genetic mutations being studied in the 20th century paved the way for genome research. While studying fruit flies, scientists discovered that certain chemicals could increase mutation rates. These became known as mutagens. Tragically, surviving victims of the nuclear bombings at Hiroshima and Nagasaki suffered radiation damage, causing scientists to study them and their descendants for decades to better understand radiation exposure.

“By the late 1970s, methods had been developed to get the sequence of DNA molecules; but you know, DNA molecules are very large, and the only way we can sequence them now with current technology is 800 base pairs, or so, at a time,” he said. “Until that time, the scientists who were studying genetic damage in the Japanese survivors and their descendants looked at genetic damage by inferring genetic damage from phenotype.”

In 1984, Nobel laureate Renato Dulbecco suggested that science should work to sequence the entire human genome, so we could compare the entire thing: our DNA, all 23 chromosome pairs, and our nucleotides. The first sponsor of the Human Genome Project was the U.S. Department of Energy, which had overseen the radiation project.

The Big Challenge

As Dr. Sadava said, modern technology can sequence 800 base pairs at a time. However, the average human chromosome has about 100 million base pairs. Furthermore, they can’t be sampled in order; they must be taken randomly. The issue is equivalent to cutting every word out of a book you’ve never read, mixing them together and then trying to reassemble the book. The answer came in looking for genetic signposts.

“There were two methods to get some sort of signposts by which we could say, ‘This particular 800-base-pair fragment’s on the left end; this one’s in the middle; this one’s on the right end,'” he said. “The first method was called hierarchical sequencing, and the second method was called shotgun sequencing.”

Hierarchical sequencing was worked on by thousands of scientists around the world and done by the government-sponsored Human Genome Project. They identified certain short sequences of DNA that appeared at certain landmarks all along the genome, like knowing that one specific character only appears in the third chapter of a book, and sequenced much of the genome that way. It took nearly 15 years.

“Shotgun sequencing was done by private industry, led by a scientist named Craig Venter,” Dr. Sadava said. “What they did was the same thing using landmarks, only they had a computer find them. What they did was take the chromosome, bust it into 800-base-pair fragments, sequence them all, feed the sequences into a computer, and have the computer line it up for you.”

An entire new field of computation was developed for shotgun sequencing and is now known as bioinformatics.

A draft of the human genome was presented in 2000, which was refined and eventually finalized and published in 2003.

Understanding Genetics: DNA, Genes, and Their Real-World Applications is now available to stream on Wondrium.

Edited by Angela Shoemaker, Wondrium Daily