Therefore , fertilization does not occur .
Thus when a sperm encounters an ovum in an animal immunized against zonae pellucidae , the sperm can not bind to the ovum because its zona pellucida has already been occupied by antibodies .
Fertilization does not occur .
Thus when a sperm encounters an ovum in an animal immunized against zonae pellucidae , the sperm can not bind to the ovum because its zona pellucida has already been occupied by antibodies .