When a DNA sample is analyzed by scientists in a DNA test, the scientists will only analyze sections or parts of the total DNA. What work with is the particular location of functional genes on the human chromosomes. Analysts so not analyze random genes but take very specific genes as subject for analysis. The total number of genes is not agreed upon by scientist but it lies anywhere between 40,000 and 70,000. Depending on whether the company you choose for your DNA test has accreditation or not, the number of genetic loci will vary. Ideally, it should be 21 loci analyzed, but this will be lower in companies that do not have accreditation DNA testing will locate the number of genetic loci shared between people to see whether there is a genetic relationship between them. The more agreement in loci between individuals the more likely it is that there is a biological relationship between the two.