Monozygotic refers to twins that develop from a single fertilized egg, or zygote, which splits into two embryos. This process results in genetically identical siblings, sharing the same DNA. Because they originate from the same zygote, monozygotic twins often have similar physical traits and may even share certain personality characteristics. These twins are commonly known as identical twins. Unlike dizygotic twins, who come from two separate eggs and sperm, monozygotic twins are always the same sex. Their identical genetic makeup can lead to interesting studies in genetics and psychology, helping researchers understand the influence of nature versus nurture.