Segments Mapped to the GrandparentsLooking at a Segment map where 3 of the 4 Grandparents have tested and there is a phased kit with the DNA of the untested Grandparent. It is easy to see that while we can be genealogically kin to someone the lines get whittled down at random.
There are several instances more so on the Paternal side where the entire chromosome copy is from one grandparent. 4(PGF) 3(PGM) 0(MGF) 2(MGM)
Granted there are still DNA segments which passed thru each of the grandparents, when entire chromosomes are passed, especially the larger chromosomes, the other lines which didn't "make the cut" are no longer represented on that particular chromosome.
(Image below is a segment map generated from my database using Genomate Pro.)
PGF(Paternal Grandfather) PGM(Paternal Grandmother)
MGF(Maternal Grandfather) MGM(Maternal Grandmother)
Paternal Phased Kit Comparisons
Running a One to One comparison of the Paternal Phased kit of my sister(full sibling) against my Paternal Phased kit
Ignore the lower part of the line(Blue & Gray) as this is Phased kit comparisons and only contains Paternal DNA
I did not include the X in the comparison because as full siblings and females we have an identical Paternal X chromosome. (Image below from comparison tools at GEDmatch.com)