Final answer:
In a pedigree where the grandfather has an mtDNA defect, one would expect matrilineal inheritance, where all of his descendants from his daughters could inherit the defect.
Step-by-step explanation:
The inheritance pattern you would expect in a three-generation pedigree, where the grandfather expresses the initial mitochondrial DNA (mtDNA) defect, is matrilineal inheritance. This is because mtDNA is passed down from mothers to all of their children, regardless of their sex, but only daughters will pass on their mtDNA to the next generation.
Therefore, all of the grandfather's children and grandchildren from his daughters would have the same initial mtDNA defect. However, this information alone does not specify the pattern of expression of this defect; for instance, whether it shows a recessive or dominant phenotype. If the mtDNA defect has a phenotype that is expressed in a manner similar to an autosomal recessive disorder, an individual would typically need two copies of the defective gene to express the disorder.