Final answer:
Dizygotic twins each have their own amnion and chorion since they come from fertilization of two separate eggs by two sperms, leading to two distinct placentas and amniotic sacs.
Step-by-step explanation:
Dizygotic (fraternal) twins always have two amnions and two chorions. This is because they develop from two separate eggs fertilized by two separate sperm, resulting in two distinct placentas. Each twin has its own amniotic sac and its own placenta, as the twins are no more identical than siblings born at different times. The amnion is a thin membrane that surrounds and protects the developing embryo in a fluid-filled cavity, while the chorion is the outermost membrane that combines with the allantois to form the fetal part of the placenta in mammals.