polyspermy, i.e. oocyte fertilized by more than one spermatozoon

slower passage of early embryo through the fallopian tube and premature zona pellucida hatching

nidation of morula into the endometrium, still enclosed in zona pellucida

a woman ovulates two and more oocytes

mitochondria are missed at all in early embryo, until blastocyst stage

mitochondria are maternally-inherited, no paternal mitochondria contribute to newly-born individuum

mitochondria include DNA, contributing to inheritance

Sperm mitochondria entrance into the egg, but they are promptly eliminated

for all early embryonic development, including zygote and 2-cell embryo

in 8 to 16-cell stage

slowly during nidation of blastocyst

already in gametes

it is implanted no earlier that is hatched out of zona pellucida

cell population counts roughly 100 cells and is differentiated onto embryoblast and trophectoderm

expansion of blastocyst and blastocoel is required for hatching and the release out of zona pellucida

it creates a cavity called blastocoel