First of all, the Y chromosomes in the DNA of the three people are consistent, indicating that you are male members of the same family. Secondly, after the DNA results of the three people are available, it is easy to determine the relationship between the three people.

Half of each set of the grandson's genes comes from his father, the son, while half of each set of the son's genes comes from his father, the grandfather.

However, the genetic comparison between grandpa and grandson does not mean that one-quarter of the grandpa’s genetic content is given to the grandson. This is uncertain.