UNDER THE MICROSCOPE

Genetic genealogy is the use of DNA tests in combination with traditional genealogical methods to infer genetic relationships between individuals.

Being in the DNA testing field for many years, I’ve been asked many times about the tests for ancestry offered online by the likes of 23andMe, Ancestry DNA, Sequencing.com etc.

Paternity testing, or more accurately, parentage testing (since it can also be used for finding genetic mothers), is a more established field. It uses short tandem repeats (STR) in specific regions in the genome to identify a common haplotype (half of the total DNA inherited from one parent) with a putative parent. 

The result of a parentage test can tell you if the man/woman tested with you is your biological father/mother with near 100 percent certainty.

Determining ancestry is more complicated. Generally speaking, we can sequence our entire genome, now more feasible and rather inexpensive (if you consider a few hundred dollars cheap), and compare it with existing databases of the companies offering the tests.

The technology for ancestry tracing uses single nucleotide polymorphisms (SNP) which are strings of nucleic acids in our DNA. The longer SNP sequences you have in common, the more you are related to each other.

Testing autosomal DNA (the 22 chromosomes besides X and Y) Y-chromosome and mitochondrial DNA provides more information for ancestry than just autosomal markers alone. The Y-chromosome is inherited through the male line; thus, it can only be used for male descendants. Mitochondrial DNA is inherited from the mother alone, but passed on to all offspring by the mother. 

If you’re interested in finding out where your ancestors came from, the results are not that clear cut. It can vary from one testing company to another, since they will have in their data depositories, different numbers of individuals from different ethnic and racial backgrounds based on how many of each race they tested. The more individuals there are in a racial database, the better the certainty of your being assigned the percentage of the race your ancestors came from. A limited number of individuals in a racial database will provide less useful information and may skew ancestry assignment.

In the case of a colleague who decided to test for her ancestry, here is what she got: Central and Eastern China 36 percent, Central and Southern Philippines seven percent, Southern China six percent, Cameroon, Congo and Western Bantu people’s two percent, Dai two percent, Southern India one percent, Spain one percent. Now, that is quite a mix, but consider that databases have frequent overlaps in DNA distributions among the races, thus the lesser percentages may not be that accurate. 

In consultations with paternity clients, I’ve often been asked if we can use hair for DNA testing. My reply has always been that in paternity cases as well as in ancestry testing, we use the best quality DNA. A cheek swab (often mistakenly referred to as saliva, but actually contains the cells from the inner lining of the mouth) is the best and most acceptable especially for immigration cases. Trace DNA is used mainly in forensic cases where you get what’s available in the crime scene.

Genetic genealogy is also used in forensics. If DNA is isolated in a crime scene but does not have a “hit” in the forensic database, the case would be considered “cold,” with no further action possible. However, if a close or even distant relative uploads his/her DNA profile online, it can be used to trace the culprit and the case becomes active or “hot” again. Many criminals have been caught this way.

An even more exciting use of forensic genealogy is the creation of a facial profile from DNA found in a crime scene. Here, the person’s DNA is matched against the different racial databases to come up with a startlingly almost-identical face as that of the person. If this advanced technique is widely used, there will be no need for an eye witness’ testimony whose memory may be faulty and can lead to the wrong person being convicted, as has happened in the past. All that needs to be done is to print or broadcast that computer-generated facial profile to catch a criminal.

The beauty of DNA as a forensic tool is that we all shed DNA anywhere we go. It can be from a glass that we drank from (which was used in a high-profile case to find the biological father of a person), or a cigarette butt discarded after smoking, or a toothbrush, hairbrush or even dandruff. What matters is that the DNA is of good quality and not degraded, even if in miniscule quantities. We have equipment that can replicate the exact DNA sequences millions of times.

So, the next time you go anywhere, think of what you’re leaving behind. It may be your ancestry that betrays you!