I did not add this but when a DNA test is done on a baby to prove who his father is---it will tell absolutely if the child belongs to whoever the mother claims is the father or not--so the some is true of a mtdna test to prove who the mother of the child really is as well. These tests on a child will tell who their mother and father truely is. It is positive proof.
This statement is not strictly accurate, as there are at least three different types of DNA tests that are used in different circumstances to confirm the possibility of paternity or maternity. Each type of test is only of value if there is a suitable test with which it can be compared. A single DNA test of any type is meaningless on its own. So, if the test is intended to confirm paternity with a specific father, for example, you need DNA samples of reasonable quality from both the father and the child.
The different types of DNA test that might be used to confirm relationships include:
(1) Y-DNA, which is inherited in the direct male line. It cannot distinguish between a father, grandfather, brother, uncle, or male cousin, but if there is no match, the relationship between suspected family members is disproved. Matches which are close, but not exact, leave the whole question open to doubt.
(2) mtDNA, which is inherited in the direct female line, though males as well as females inherit it from their mothers. It cannot distinguish between mother, grandmother, sister, aunt, or female cousin, but if there is no match the relationship between suspected family members is disproved. Again, close matches are suggestive, but not proof.
(3) A paternity test, using autosomal DNA values at standard sites on about 13 different chromosomes (CODIS values). These are internationally standardised and are frequently used in forensic tests, paternity or maternity tests, and tests of siblings. Although exact matches are usually diagnostic of relationships, near matches are much less certain, as people from similar geographic backgrounds can have similar DNA values, so results can often be inconclusive.