Genetic marker variants are specific, identifiable differences within a person’s DNA sequence. These variations act like distinctive signposts along chromosomes. Their value comes from their precise location and ability to be tracked across generations or within a population. They help scientists explore various aspects of biology and human characteristics.
What Are Genetic Markers?
Genetic markers are specific DNA sequences that vary among individuals. These variations are often found in non-coding DNA regions, meaning they do not directly provide instructions for making proteins. Their specific location on a chromosome makes them useful as observable tags.
The most common type of genetic marker is the Single Nucleotide Polymorphism (SNP). A SNP involves a change in a single DNA building block, or nucleotide, at a specific position in the genome. For example, at a certain location, one person might have an adenine (A) while another has a guanine (G). Other markers include Short Tandem Repeats (STRs), which are repetitive DNA sequences where the number of repetitions varies between individuals.
Identifying Disease Risk
Genetic marker variants can offer insights into an individual’s predisposition to certain health conditions. This connection often arises due to linkage disequilibrium, where a marker variant is located very close to a specific gene on a chromosome. This causes them to be inherited together, allowing the marker to serve as an indicator for the nearby gene or a DNA region associated with a trait or condition.
A marker variant indicates a statistical correlation rather than a direct cause of a disease. For instance, certain variants of the APOE gene, such as APOE e4, are associated with an increased risk of developing late-onset Alzheimer’s disease. While carrying the e4 variant raises the probability of developing the condition, it does not guarantee its onset, and many individuals with the variant never develop the disease. The marker acts like smoke indicating a nearby fire, rather than being the fire itself.
Applications in Forensics and Ancestry
Genetic marker variants have uses beyond health insights, extending into forensic science and personal ancestry tracing. In forensic investigations, scientists analyze Short Tandem Repeats (STRs) found at specific genome locations. The unique number of repetitions at multiple STR locations creates a distinct “DNA fingerprint” for each individual, which can be matched to samples found at crime scenes to identify suspects or victims.
The frequency of specific genetic marker variants can differ among populations that have historically lived in different geographical regions. By analyzing an individual’s pattern of these markers, scientists can estimate the proportions of their ancestry originating from various parts of the world. This forms the basis of consumer ancestry testing services, providing insights into historical migration patterns and family origins.
How Scientists Study Marker Variants
Scientists employ advanced methods to identify and analyze genetic marker variants across large populations. A prominent research approach is the Genome-Wide Association Study (GWAS). In a GWAS, researchers scan the genomes of thousands of individuals to find marker variants that occur more frequently in people with a particular disease or trait compared to a control group.
These studies are made possible by sophisticated technologies such as DNA sequencing and microarrays. DNA sequencing allows scientists to determine the exact order of nucleotides in a person’s entire genome or specific regions of interest. Microarrays are tools that can rapidly detect the presence of hundreds of thousands to millions of known marker variants simultaneously.