What term describes twins that are genetically identical and derived from a single ovum?

The term that describes twins that are genetically identical and derived from a single ovum is "monozygotic twins." This type of twinning occurs when a single fertilized egg, or zygote, divides into two separate embryos during the early stages of development. Since both embryos originate from the same zygote, they share the same genetic material, resulting in twins that are genetically identical, which is why they are often referred to as "identical twins."

In contrast, fraternal twins (also known as dizygotic twins) arise from the fertilization of two separate ova by two separate sperm cells, leading to genetically unique siblings, just as any other siblings born at different times. Non-identical twins is not a formal term used in biological classification, but it generally refers to fraternal twins as well. The term dizygotic specifically highlights the fact that these twins are not identical genetically. Thus, "monozygotic twins" is the specific and correct term for twins that are genetically identical and originate from a single fertilized egg.