ES cells were pretreated with rhodamine 6G to removed endogenous mitochondria and mtDNA prior to fusion with B82mtA11 mitochondria donor cells (derived from the L929 fibroblast cell line; C3H/An mouse strain) containing a G-to-A transition at position 13,997 (g.13997G>A) resulting in the substitution of proline 25 with leucine (p.P25L). (J:164405, J:164565)