altering a swab test

[736610]

The alledged father and I met to have a DNA test.  I am the child in question.  Prior to performing the buccal swab DNA test the man went into the bathroom and then came out and spit a large amount of saliva.  He then proceeded to just suck on the swab.  He did not wipe the inside of his cheeks.  Is it possible to place the saliva and cheek cells of another person into ones mouth and then place the buccal swab into the saliva to absorb the saliva and cells.  I have not felt comfortable about this test since it was done.  Needless to say, the result came back and said he can be ruled out as my father.  Have you ever heard about anybody tampering with tests like this.  

[lilywhite]

I'm a geneticist.  It's extremely unlikely that he could suck on the swab and not have some of his own saliva get onto it.  In fact, it's pretty much impossible.  Police take cigarette butts all the time and extract DNA.

The only thing that would happen is that there would be two sets of DNA which would be obvious to the person reading the test and would result in an invalid and contaminated test.