Y Chromosome DNA Testing
It is helpful when the fathers sample is not available or in cases of family reconstructive DNA testing.
This type of testing only works if there are no breaks in the paternal family tree. Such as a fathers full brother and the child of that father would share the same Y-chromosome.
While the mother's brother and the child would not. This type of testing can go back many generations as long as there are no breaks in the paternal family tree.