Which term describes twins resulting from two different eggs?

Fraternal twins are “dizygotic,” meaning that they developed from two different eggs fertilized by two different sperm cells, while identical twins are “monozygotic” i.e., they developed from a single fertilized egg that split. The likelihood of identical twins is the same around the world — about 3 in 1,000, while the incidence of fraternal twins varies by geography and ranges from 6 to over 20 per 1,000 deliveries.

Zygosity refers to the similarity between the genomes of each twin. Fraternal twins are dizygotic, meaning that they developed from two different eggs fertilized by two different sperms. Their genetic code is as similar (or dissimilar) as any other siblings.

Identical twins are monozygotic, meaning that they developed from the same fertilized egg, and so have nearly identical genetic code. They almost always have the same gender and many of the same physical characteristics (phenotypes). However, they may develop some genetic differences after the zygote splits, due to mutations in the DNA.