The Evolution of DNA Profiles

Nearly forty years ago, a revolution that would alter our understanding of genetics began quietly in a lab at the University of Leicester (UK). A team of scientists headed by Dr. Alec Jeffreys had been studying highly variable regions of human DNA for several years. Sometimes during the DNA copying process, the enzyme responsible can slip on the template and "stutter". Jeffreys and his team noted that the resulting "minisatellites" - short regions of repetitive DNA - had a high amount of variability from person to person. They used a technique of cutting the DNA with different enzymes before running it on a gel to visualize this variability. In September of 1984, while analyzing the DNA of his technician and her parents, Jeffreys had a eureka moment and realized their approach had created the first DNA fingerprint or profile. 

The first time this technique was used in a forensic science capacity was in 1985. In November 1983, a 15-year-old girl Lynda Mann was found sexually assaulted and strangled to death in a field not far from her home in the village of Narborough in Leicestershire. A police officer who had heard about Jeffreys work at the University asked if it might be possible to create a DNA fingerprint from the semen left behind at the scene. Before long, another 15-year-old Dawn Ashworth was found sexually assaulted and murdered in a manner similar to Lynda in the neighboring village of Enderby. Jeffreys confirmed that the same individual was responsible for both attacks and eliminated the initial suspect. Police collected a DNA sample from all the men in the area to screen for the perpetrator. No one was a match, leaving investigators perplexed.

Finally in August of 1987 there was a break in the case. A coworker of Colin Pitchfork told other colleagues at a pub that he had provided a DNA sample for Colin because Colin told him he didn't want to be "harassed by the police over prior convictions for indecent exposure". One of the coworkers reported this admission to the police. Law enforcement promptly found the real Colin and got a DNA sample, which matched the semen found at both crime scenes. Colin Pitchfork was convicted and jailed in 1988 with a minimum sentence of 30 years. He was released in 2021, but returned to jail 2 months later for violating parole by approaching a lone woman. Just this week, the parole board has once again deemed Mr. Pitchfork suitable for release. There has been considerable public outcry in response to this decision.

While the basic tenet of Jeffreys approach to DNA profiling (exploitation of variable regions of DNA) has remained the same, the technique has evolved to focus on smaller segments of repetitive DNA known as short tandem repeats or STRs. Scientists amplify dozens of STRs scattered around the human genome to determine how many repeats are present for that loci or location. Rather than running the DNA mixture through a gel like Jeffreys did, the samples are now run through a very small capillary tube and the results are captured by software on the computer attached to the machine.

Remember that for each STR loci there will be two copies analyzed because each parent contributed one allele or version of the STR to their child. At present, the FBI recommends examining a minimum of 20 STR loci to create a DNA profile. Due to the number of loci analyzed, the likelihood of someone having the exact same pattern of repeats as another individual is so extremely small as to essentially be improbable. The exception to this, of course, is monozygotic or identical individuals. An example of what a modern DNA profile looks like is below (Source: NIST).

Once an STR profile has been generated, it can be compared against other STR profiles. CODIS is the FBI's software program that runs a variety of DNA databases. For example, there are separate databases that fall under the CODIS umbrella for criminal offenders and missing persons.  

DNA profiling has radically changed how we identify people over the past 40 years. It allowed for effective paternity (and maternity) testing and revolutionized forensic science. No doubt the methodology for developing a DNA profile will continue to be improved upon in the future. There are already rumblings that single nucleotide polymorphism (SNP) profiling may be the next wave. But one thing is certain - DNA profiles are here to stay.

New Year, New Me

Today is the first day of 2023. I have been thinking a lot lately about how much I have associated my identity with my employment over the course of my life. I will be turning 45 this year. For over 15 years now, I've been a high school science teacher. It took me quite a few years to get comfortable with saying that, after having spent over 8 years becoming a practicing bench scientist. 

In time, I became proud to say that I was a biology teacher. But in the past 5 years of my teaching career, I have spent very little time actually teaching biology. The bulk of my courses have been forensic science, a course which I volunteered to finish writing the curriculum for in 2012-2013 because the coworker who originally proposed it was planning a move into supervision. 

Teaching forensics has been a great creative challenge for me. I needed to learn more about chemistry, physics, psychology and criminal justice to do the subject justice (pun intended). But I will say that it also caused me to have an identity crisis. How could I call myself a biology teacher if I rarely taught the subject? How could I connect to the identity that helped me accept that I'd left the bench and was no longer a researcher? I had a conversation with my very supportive boss more than a year ago explaining this growing internal panic. I'm not ashamed to admit that I got teary eyed. It's not that I didn't want to teach forensics anymore. I just didn't want it to be the only thing I was teaching. 

My boss suggested I write a curriculum for a new course. And so I did. Last fall, I planned out three technically - either two half year courses or one full year course covering genetics, molecular biology and biotechnology in greater detail than Biology 1 or AP Bio could cover. Unfortunately, budget cuts and staff reduction seemed to temporarily derail any efforts to develop new courses. I was disappointed, but that disappointment was tempered by learning that I would be able to teach two sections of Biology 1 in the fall.

After not teaching biology since the 2018-2019 school year, I was very excited for my 16th school year to begin. Redoing my Biology 1 course to reflect the sequencing and increased emphasis on NGSS pedagogy adopted by my colleagues over the past 5 years was a challenge I was looking forward to. And I will say that things were going pretty normally. Until late October. A short email changed everything.

It said "We got funding for the grant. Can you call me?"

For this to make sense, I need to go back about 2 years to the winter of 2021. I'd been trying without success to volunteer to do genetic genealogy for forensic cases since 2020. I applied to the DNA Doe Project and got no response. I attended many forensics webinars and asked the presenters about what to do but was met with vague non answers. I asked my sister (the forensic DNA analyst) if her lab worked with volunteers, but they field all of that kind of work out to Parabon. So as a last effort, I emailed the director of the county crime lab. We'd interacted several times before trying to make a forensics field trip work. 

She said that yes, they had just begun to use the technique on cold cases and were using outside contractors to do the genealogy. She was writing for a federal grant to get funding for these projects and said that she would be happy to work with me as a volunteer or independent contractor. She was hopeful they'd get an answer on the grant by the summer. That didn't happen. In October 2021, the director contacted me to say the grant application was rejected. But she said that she would try again and keep me updated.

Fast forward to the last week of October 2022. I finally call her on Friday after school to congratulate her about getting funding. She says, "Well, it's potentially good news, bad news. Good news is we have the funding. But the grant doesn't allow for volunteers or outside contractors. It's written with the expectation of a full time lab employee in house doing the work." I'm sure she could hear the disappointment in my voice when I said "Oh." She quickly said, "What I'm trying to say is that if you want the job, it's yours."

I will admit that the decision wasn't an easy one. And it may have resulted in quite a few tears being shed. But after a couple of weeks of weighing everything and discussing the topic with my immediate family ad nauseam, I accepted. The official print offer came just after Thanksgiving. I sent my resignation to the Superintendent on Monday December 5th, told my students and science colleagues what was happening on Thursday December 8th and my departure was announced at the Board of Ed meeting on Tuesday December 13th. My last day as a teacher at the school that's been home for over 15 years is February 3rd.

Come Monday February 6th, I will be working full time as a data analyst (aka genetic genealogist) for the Union County Prosecutor's Office Forensics Lab. I will be collaborating with the homicide detectives to identify victims and generate suspect leads in cold cases. 

I know that this is a once in a lifetime career opportunity. It's thrilling and bittersweet at the same time. It's made me fundamentally rethink who I am as a professional. I am a scientist, whether I am at a bench or not. I am an educator, whether I am in a classroom or not. I have made a career of being a public servant in so many different capacities. I am more than any job title I may hold. And now I'm excited to step into the unknown of 2023, fully authentically me.