If the digest is complete, how many pieces of DNA would you expect to see if you separate the DNA by electrophoresis and if the pieces can be separated on the agarose gel. Because DNA is negatively charged at neutral pH, it moves in an electric field. The large fragments, having more negative charges, move more quickly through the agarose than the smaller ones do. Heating double stranded DNA to 100 o C denatures the hydrogen bonds holding the two strands together, but does not break the covalent bonds of the DNA backbone. These are stretches of DNA with repeating sequence.
Different people can have different numbers of the repeat but the repeat number is inherited.
So, you can think of the sequence you get from your mother and the one you get from your father as exhibiting co-dominance when the DNA is analyzed by restriction digest and the DNA pieces separated by electrophoresis. Your maternal grandmother has 9 copies of the repeat on each chromosome. Your dad has 22 copies of the repeat on at least one chromosome. Your mom has 9 copies of the repeat on at least one chromosome. Your mom has 15 copies of the repeat on at least one chromosome.