DNA testing, at least to some degree, has been around for decades. However, direct-to-consumer DNA testing, or “consumer genetics,” has exploded in popularity in the last few years. In fact, the market is expected to reach a whopping $1990 million USD by the end of 2024 1. Numerous companies offer commercial DNA testing, each operating in a slightly different market niche. What is DNA testing, and what can it tell us about our ancestry?
What is DNA?
To understand how DNA testing works, we first have to understand what DNA is. DNA stands for deoxyribonucleic acid and is the molecule that provides all the instructions to build and function an individual. DNA is inherited from both parents (50% from your mother, 50% from your father) and is essential for the continuation of life.
DNA is a long molecule that forms a double-stranded helix structure. Each strand of DNA is a long chain that is made up of four repeating units. These repeating units are called bases or nucleotides. They are represented as a four-letter code: adenine (A), thymine (T), cytosine (C), and guanine (G). Each base pairs with its complementary partner to connect the two strands in the center of the double helix. A pairs with T, and C pairs with G.
The order or “sequence” of these bases determines all the activities in the cell. The cell first copies the sequence in the DNA to an intermediate molecule called RNA. The RNA sequence is then translated into a protein sequence. As a result, the DNA sequence determines the structure and function of proteins, which carry out virtually every job in the cell. Therefore, the DNA sequence and any variation found within it is a rich source of information about an individual.
DNA tells us a lot about how the cell functions. But, more importantly for genealogy research, it also holds vital insights into our ancestry, acting as a record of our heritage over generations.
DNA testing involves “sequencing” the DNA, that is, determining the order of each of the bases at particular sites of interest. Sometimes, during DNA testing, the entire genome (i.e., all the that makes an individual DNA) is sequenced, but more commonly, DNA testing involves analyzing particular portions of the DNA that contain valuable information.
What can DNA testing reveal?
DNA is passed from parents to offspring. It provides all the information for the function of every cell, tissue, organ, and system. Thus, DNA testing can reflect a lot of information about an individual.
Variation in DNA can reflect familial relationships, ethnic background, migration patterns, and ancestry. DNA sequences can also be used to infer disease-associations and likely responses to treatments. Additionally DNA is often used to provide insights into traits such as potential athletic ability, personality features, physical characteristics, and to guide health and wellness regimes. The links between DNA and these features are usually based on studies that have determined that specific DNA variants are more common in the population that possesses certain traits. For example, a particular change in the DNA sequence is more common in those with British ancestry.
Some connections between DNA and specific characteristics made by commercial genetic testing companies have more scientific backing than others. For example, certain diseases are strongly linked with certain changes in the sequence of specific genes. However, some testing is considered unreliable for health-purposes by clinicians. This is due to the potential for false positives and false negatives, and discrepancies over whether a genetic variant is truly linked with a disease 2,3. The vast majority of these health tests are not FDA approved 4.
What are the types of DNA testing?
Various types of DNA testing can be carried out. The choice of which is employed is largely dependent on what the DNA testing is aiming to uncover. Another consideration is the cost, which can vary widely between different methods.
The most common type of analysis in the direct-to-consumer DNA testing market is targeted SNP analysis. SNP stands for single nucleotide polymorphism and describes sites at which DNA sequences change by a single base. SNPs are a type of normal variation in the human population. Therefore, SNPs are regions in the DNA that are commonly different between individuals and can be used for identification purposes
Certain SNPs can be used to predict certain features of an individual. For example, whether they have genetic variants associated with an increased risk for heart disease. SNPs can also determine an individual’s ethnic background.
Typically, DNA testing companies will have a pre-defined set of SNPs that they sequence in the DNA. Specific variation in these SNPs is linked with an increased or decreased likelihood of possessing a particular trait2. Some variants are also associated with certain ancestries or ethnicities 5.
The Y chromosome is only present in males. Therefore, analyses of sequences on the Y chromosome can be useful for determining male lineage. The Y chromosome is particularly well suited for tracing ancestry. This is because the DNA on the Y chromosome accumulates changes much more slowly than other chromosomes over time as they are passed down through generations. This means that sequences present on the Y chromosome can act as markers for the origins of your ancestors. The Y chromosomes of males and their direct relatives are virtually identical.
Y-DNA testing usually involves assessing short tandem repeats (STRs) or SNPs, as described above. STR analysis determines differences in the numbers of short repeats, which vary between individuals but are similar between closely-related individuals. This means they can be used to link male relatives 2,6. These tests can identify the specific “haplogroup” that a male belongs to, which represents a particular set of shared DNA variants, reflecting the geographical movement of your male ancestors.
Mitochondrial DNA (mtDNA) analysis assesses mitochondrial DNA, which is maternally inherited. Mitochondria are small organelles present inside every cell. They have their own genome, which is very small. It is maternally inherited mostly due to size: the egg is much much larger than a sperm. This means it contains many more mitochondria – about 100,000 times more. When the egg and sperm combine, the sperm mitochondria make up so little of the total combined mitochondria (and are then degraded), so only maternal mitochondria remain. Maternal DNA variation can, therefore, be used to trace your ancestry specifically on your mother’s side.
DNA testing is an excellent addition to the genealogy toolkit. As more people submit samples for testing, scientists can build a greater understanding of how DNA relates to ethnic groups and ancestry. DNA brings a degree of precision and certainty to genealogy research. Together, traditional genealogy and genetics can help to find missing pieces of your ancestry puzzle.