Fraternal twins, also known as dizygotic twins, occur when two separate eggs are fertilized by two different sperm cells during the same menstrual cycle. This results in two genetically unique siblings who share about 50% of their DNA, similar to regular siblings born at different times. Fraternal twins can be of the same sex or different sexes, and they may or may not look alike. Factors such as genetics, maternal age, and the number of previous pregnancies can influence the likelihood of having fraternal twins.