Job Description:

A forensic DNA analyst works mostly in a forensics lab, where they perform DNA tests on biological material that police investigators submit to the lab. The analyst also interprets the results of the DNA tests.

Education:

DNA analysts are required to have at least an associate’s degree in chemistry, biology, or forensic science, but a bachelor’s degree or in some cases, a master’s degree is preferred. With a bachelor’s degree and two years of experience, a person can choose to take a test to become certified with the American Board of Criminalistics.

Qualifications:

In addition to a college degree, in most cases, a forensic DNA analyst must have experience doing DNA casework (for example, collecting samples), be familiar with lab equipment, and have strong verbal and written communication skills.

Additional Information:

The DNA analyst must be prepared to give expert testimony in court when called on to do so. They must also be able to periodically check the reliability of lab equipment and procedures and to help train new analysts hired by the lab.

Salary:

The average salary for a forensic DNA analyst in 2017 was $37,000 to $85,000.

Investigators could also collect and examine blood samples from a crime scene—a technique called blood-typing. They might find some traces of type B-positive blood and some traces of type A-positive blood at a murder scene, for example. After taking a sample of the victim’s blood and finding that it was B-positive, they could conclude that the A-positive blood most likely came from the murderer. However, this technique is limited in its usefulness. First, hundreds of millions of people in the world have A-positive blood, so in theory, anyone with A-positive blood living in the area where the murder occurred might be the guilty party. Additionally, sometimes multiple blood samples at crime scenes get mixed together. If types A and B combine, it can often look like blood type AB, making blood-typing in that case useless.

What crime investigators needed was a forensic technique that was far more precise and conclusive than either fingerprinting or blood-typing. They needed a way to zero in on and more firmly identify a culprit from among thousands of potential suspects. This is what they got when DNA profiling was introduced in the mid-to-late 1980s. The technique is also referred to as DNA fingerprinting, genetic fingerprinting, DNA analysis, DNA forensics, and DNA testing.

Whatever one chooses to call it, the use of DNA to solve crimes has revolutionized police work and legal systems in countries around the world. This is because of the special nature of DNA, a core part of the genetic blueprints of living organisms. Because the DNA of everyone in the world is unique, one person’s DNA, in theory, can be differentiated from the DNA of everyone else. This gives forensic scientists, police, lawyers, and judges a far better chance of identifying each individual present at a crime scene with a high degree of certainty and making sure these lawbreakers are punished. Therefore, the discovery of DNA and its application to crime solving make up one of the great triumphs of modern science.

DNA Discoveries and Heredity

The development of DNA profiling began in 1952. That year, two American researchers, Alfred Hershey and Martha Chase, made an important discovery. Working in their Cold Spring Harbor Laboratory in Long Island, New York, the researchers studied a substance found in the bodies of all living things: DNA. Between 1869 and 1950, a number of researchers around the world had isolated DNA and studied it. However, no one was quite sure exactly what its purpose was. Until Hershey and Chase’s breakthrough, the connection between DNA and heredity—the passing on of traits from one generation to the next—had not been proven conclusively (without a doubt).

The most popular theory at the time was that certain proteins controlled heredity. However, Hershey and Chase made a vital discovery: They proved that DNA is a genetic material carrying some of the blueprints of life. The exact manner in which DNA determines the genetic makeup of people and animals was still uncertain at this point because the structure of the DNA molecule remained a mystery.

Hoping to solve this mystery, American scientist James D. Watson and English scientist Francis Crick began intensively studying DNA. At the same time, British scientists Maurice Wilkins and Rosalind Franklin began working on a similar project. At some point between 1951 and 1953, Wilkins showed Watson X-ray photographs of DNA that Franklin had taken, along with her notes. Seeing them, Watson pieced together the solution. Watson and Crick published their findings in 1953 without crediting Franklin’s work. Their article correctly proposed that the DNA of people and animals is stored in the nucleus, or center, of nearly every cell in the body. DNA molecules are bigger than other molecules and uniquely shaped. Each DNA molecule consists of two long strands of genetic material. One strand comes from a person’s mother and the other from their father. In that way, every person inherits some genetic information from each parent. Franklin published her work in a supporting article in the same issue of the journal, but history gave Watson and Crick all the credit.

How Many Helixes?

The two strands inside each DNA molecule twist around each other, forming a winding spiral that scientists call a double helix. This double helix looks like a twisting ladder because the two strands are connected in thousands of places by little rungs. Each rung is composed of two parts, called nucleotide bases, and each grouping of two is called a base pair. In all, a typical DNA molecule has about 3 billion base pairs, for a total of about 6 billion bases.

DNA testing can help determine the relationship between two people. A testing kit is shown here.

These bases are always made up of the same four chemicals—guanine (G), cytosine (C), thymine (T), and adenine (A). The chemicals arrange themselves on the DNA ladder in varying patterns, called sequences, which can be short or long. One example of a short sequence is AGCTCAATCG.

The chemical sequences that extend through the base pairs of a DNA molecule form small bits of genetic information, and each of these bits determines part of the complex blueprint for constructing the body of one person or animal. These pieces or sections of DNA that contain all the information needed to make these changes are called genes. Thus, each gene consists of a series of chemical sequences that exist alongside one another on the double helix, and together they perform a single genetic task. Genes can take multiple forms, which are called alleles. Everyone inherits one allele for each gene from their mother and one from their father. For example, every human has a gene for hair color, but not everyone has the same allele. If someone’s mother has brown hair while their father has blond hair, the person will inherit the brown hair allele and the blond hair allele. They cannot inherit a red hair allele unless a blood relative in their family has red hair.

Many people believe each gene has a specific task, but researchers now know this is not always true. Some traits, such as eye color, are monogenic, or controlled by just one gene. Others are polygenic—requiring multiple genes to work together. Even something as simple as whether a person is right-handed or left-handed is polygenic. Most traits are also influenced by a person’s environment. According to the website Learn.Genetics,

Multiple studies present evidence that handedness is controlled by many genes—at least 30 and as many as 100—each with a small effect; many are linked to brain development. Environment also plays an important role: some cultures actively discourage left-handedness .5

Sometimes traits that are monogenic show up in a person as a type of disorder or disability. For example, color blindness is monogenic, and so is a very rare type of diabetes called neonatal diabetes mellitus (NDM), which is diabetes that an infant is born with. Other diseases and disorders, such as the more common type 1 and type 2 diabetes, are polygenic.

The ability to understand and distinguish individual genes and alleles is essential in DNA profiling. All the base pairs, chemical sequences, genes, and alleles in the DNA of humans add up to the genetic code—what makes each individual person who they are. The complete human genetic code is called the human genome.

Sir Alec Jeffreys and the 0.1 Percent

In the years following the work of Franklin, Wilkins, Watson, and Crick describing the DNA double helix, it became clear that close to 99.9 percent of the human genome is identical in all people. Therefore, only one-tenth of 1 percent of the sequences, genes, and alleles are different. When it comes to genes, people are more like everyone else in the world than they are different.

However, these small differences are what distinguish one person from another. One-tenth of 1 percent may not sound like much, but it consists of about 3 million base pairs. When these are arranged in different ways, they can produce billions or trillions of possible variations. This is how people can be so diverse despite having 99.9 percent of the same genetic sequencing.

It was this one-tenth of 1 percent and its many potential variations that attracted the interest of the father of DNA profiling, English geneticist Sir Alec Jeffreys. Jeffreys began working at a lab at the University of Leicester in 1977. In the years that followed, he and his colleagues studied genes and how they evolved and changed. This led him to look at sections of the DNA double helix that seemed to be different in different individuals, called highly variable regions. Within these areas are short chemical sequences that came to be called minisatellites.

Jeffreys searched for ways to better observe these minisatellites. “We made a probe that should latch onto lots of these minisatellites at the same time,”6he explained. Then, in September 1984, the researchers used an X-ray machine, like that used by dentists and doctors, to take a picture of what the probe had revealed. Jeffreys recalled,

I took one look, thought, “what a complicated mess" then suddenly realized we had patterns ... There was a level of individual specificity that was light years beyond anything that had been seen before ... Standing in front of this picture in the darkroom, my life took a complete turn.⁷

Sir Alec Jeffreys (shown here) is responsible for a major breakthrough in scientific DNA testing.

Jeffreys and his colleagues recognized that they had done more than create images of areas of DNA variability, although even that was certainly a difficult and important feat that would advance the course of modern science. What Jeffreys’s team had done was recognize that the patterns of minisatellites on the X-ray could be used in other areas of science, including forensic science. In particular, since these areas of DNA variability were different for each person, they could be used to distinguish one person from another. In a later interview, Jeffreys explained,

The implications for individual identification ... were obvious ... It was clear that these hypervariable DNA patterns offered the promise of a truly individual-specific identification system ... For the first time [there was] a general method for getting at large numbers of highly variable regions of human DNA. Also, almost as an accidental by-product, it suggested approaches for not only developing genetic markers for medical genetic research, but for opening up the whole field of forensic DNA typing.⁸