When testing without the mother, the probability of paternity is 98.2896% - inconclusive for paternity. Now, add the biological mother's sample to the DNA paternity test:
| Locus | Biological Mother (not tested) |
Alleged Father | Child | Parentage Index |
|---|---|---|---|---|
| D2S1338 | 8, 10 | 12, 13 | 10, 12 | 3.489 |
| D2S1358 | 14, 17 | 8, 11 | 11, 14 | 5.114 |
| D8S1179 | 15, 19 | 21.2, 32 | 19, 21.2 | 3.619 |
| D19S433 | 8, 12 | 15, 18 | 12, 15 | 15.309 |
The probability of paternity increases to 99.9541%. Why? In the first example, one of the two alleles from the child and alleged father match at each location. However, we don't know which of the child's markers comes from his mother and which must come from his father. By testing the child's mother, we see which of the child's markers must have come from the mother and which must have come from the father.
With the mother, the paternity calculation is increased. Not only does the child match the alleged father, but the match is with the marker that must have come from the child's true biological father (since we can see which marker came from the child's mother). In fact, the index value is higher at each location because the biological mother participated in the DNA test.
Now the result is strongly conclusive, all because the mother participated in the DNA test.
