Multiple choice What part of the embryo is the origin of the primordial germ cells? Gonadal ridge Endoderm of the yolk sack Coelomic epithelium Extraembryonic mesoderm Genital tubercle Reveal answer Fill a bubble to check yourself B Correct answer Explanation In gonadal development, undifferentiated primordial germ cells arise from the endoderm lining the yolk sac. These germ cells detach and migrate dorsally to reach the coelomic epithelium lining the genital ridges.