A 28-year-old primigravida from rural Tamil Nadu presents at 14 weeks of gestation with vaginal bleeding and passage of grape-like tissue per vaginum. Pelvic ultrasound shows a "snowstorm" appearance with no fetus and bilateral enlarged ovaries. The pathological specimen shows the structure marked **A** — grape-like hydropic vesicles with central cistern formation and circumferential trophoblastic proliferation. Which of the following best explains the pathogenesis of this condition?