Final answer:
A mother conceives dizygotic twins when two different eggs are fertilized by two different sperm, resulting in fraternal twins that are no more identical than siblings born at separate times.
Step-by-step explanation:
A mother will conceive dizygotic twins when both eggs are fertilized by different sperm. During an ovulation cycle, it is possible for two eggs to be released and both may be fertilized, leading to the formation of two zygotes that implant and develop into fraternal twins. Unlike monozygotic (identical) twins that result from the division of a single zygote into two embryos, dizygotic twins come from two separate eggs and sperm, making them no more identical than siblings born at different times.