What's the difference between DNA profiling and genetic testing?

DNA profiling looks at repeated nucleotide sequences within inactive genes. Examining as few as 16 different locations in human DNA can yield very clear information on whether or not a DNA sample belongs to person A. This is how DNA analysis is used in forensic profiling. This is also what is now commonly referred to as a "DNA fingerprint". By the way, the techniques have changed in the past 10 years or so, so results from 10 years ago may not be comparable with results of today's analyses.

Paternity testing done by profiling requires samples of the purported father and the "child" (that is, the presumed offspring). The mother's DNA is not necessary, but can be helpful. In this case, a sample from each person can be profiled and the profiles compared visually or electronically. Alternatively, the samples can be tagged with two different fluorescent markers, mixed and analyzed--looking for similarities and differences. Lineage testing (maternal, paternal, ethnic) uses the latter technique, which is more prone to error.

Genetic testing for particular gene sequences (active DNA, for example, a particular cancer gene) can be done with DNA directly or by examining DNA's "expression"--messenger RNA. Here, the techniques are much more complex and subject to error and variations in interpretation.

Then we get to the most complex and weakest aspect of genetic testing--inferring phenotype (appearance, function, likelihood of disease, etc.) from genotype. Here, there may be lots of literature and hype, but little clear connection between a test and the prediction of a person's future. Even "known" genes may have many variants and results without supportive genetic counseling can cause more harm than good. 

Marie Godfrey, PhD