Practice question

Paternal mitochondria enter oocyte cytoplasm at fertilization localized in midpiece, but they are actively eliminated shortly thereafter to ensure maternal uniparental mitochondrial inheritance. Ubiquitination of sperm mitochondrial proteins, recognition by oocyte autophagy machinery, mitophagy and proteasomal degradation remove them before first cleavage divisions. Occasionally low-level paternal mtDNA leakage occurs but is exceptional. Therefore mitochondria do not persist, merge or form embryonic population; embryonic mitochondria derive entirely from oocyte pool amplified during oogenesis, supporting high ATP demand of early development while avoiding heteroplasmy conflicts and protecting mitochondrial genome integrity.