A male mouse embryo failed to develop into reproductive adult because of the expression of defective IGF2 protein (mutant allele of igf2gene, which is known to be maternally imprinted). Given that this mutation on igf2gene is very rare among mice in the population (i.e. it is unlikely that an individual inherit two copies of the mutant allele), which grandparent of the embryo is most likely to carry this mutation? Explain the answer with a pedigree diagram showing the genotype of the grandparents, parents, and embryo and the type of imprinting for each.