FIG. 3.

Defining the critical developmental threshold of mtDNA copy number. Mitochondrial DNA quantification of biopsied blastomeres from cleavage-stage (8-cell) embryos was performed to estimate mtDNA content in cleavage-stage embryos before transfer to surrogate recipients. Embryos were grouped into low-copy or high-copy groups and then transferred to separate uterine horns of the surrogate. In some cases, it was possible to assign copy number in individual embryos by examining the heteroplasmy measurements in the developed postimplantation embryo. Normal, stage-appropriate morphological development was scored as positive; aborted and developmentally delayed embryos were scored as negative. All images were acquired under the same original magnification (×25).