How a few DNA regions become a profile
The repeated sequences used in profiling are called short tandem repeats, or STRs: tiny stretches of DNA copied one after another. The number of copies can vary from person to person. At each selected location—called a locus—a person typically carries one version inherited from each biological parent, so the result may show one repeat count or two.
A lab does not need to read a person’s entire genome. It makes many copies of the chosen STR regions from a sample, then separates the resulting DNA fragments by length. Because fragments with more repeats are longer, their lengths reveal the repeat counts at those locations. The collection of counts forms the profile.
Why several locations matter
One repeat count is not especially identifying: many people can share it. The power comes from examining multiple loci. Each additional count adds another point of comparison, and the particular combination is far less common than any one feature alone. That makes STR profiling useful for comparing biological samples, such as checking whether DNA from a scene is consistent with a person’s reference sample.
A profile is not a name or a complete account of someone’s biology. It is a pattern to compare, and its strength depends on how many regions were successfully measured and how common that combination is in the relevant population. A small or mixed sample can produce incomplete or harder-to-interpret results. The method’s practical advantage is that it can extract a powerful comparison from a limited set of carefully chosen DNA regions—without sequencing the whole genome.
