How does DNA testing work?

DNA testing works by detecting certain parts, or 'markers' in the DNA molecule that are known to vary greatly between people who are unrelated, but are shared by people who are related. Cellmark uses a 24 marker test (one of the markers is only found in males, and another is used to determine biological sex) to compare the DNA from the people being tested and to assess their biological relationship.

The original DNA techniques for paternity testing were developed by Professor Sir Alec Jeffreys at the University of Leicester in 1984. Using this technology Cellmark became the UK’s first DNA paternity testing company in 1987. Today the technology has evolved allowing us to provide quicker, cheaper paternity tests but still with the same high levels of certainty that only DNA testing can provide.

The DNA process used today is called Short Tandem Repeat (STR) profiling, a highly sensitive process that was originally developed for forensic analysis. DNA is extracted from each mouth swab in Cellmark’s UK laboratories and the STR markers are then detected and measured. A DNA profile is the combined result of multiple STR markers. The DNA profile is shown in the test report as a series of numbers, which represent the size of the individual STR markers that have been tested.

A child inherits half of its DNA from each parent. Cellmark’s scientists will compare the STR markers in the child’s profile with the alleged parent(s) to determine if they are related. Testing will either exclude the man from paternity with 100% certainty, or will provide a probability of paternity which is usually in excess of 99.9999% (if the child’s mother is included in the test).

When carrying out a paternity test, including a sample from the mother (as well as from the child and alleged father) will always provide a more conclusive result.