Identical and fraternal twins differ mainly in how they form and how similar their genes are. Identical twins come from one fertilized egg that splits, while fraternal twins come from two separate eggs fertilized by two different sperm.

Basic definitions

  • Identical twins (monozygotic) form when a single fertilized egg (one zygote) splits into two embryos.
  • Fraternal twins (dizygotic) form when two separate eggs are released and each is fertilized by a different sperm cell.

Genetics and appearance

  • Identical twins share (almost) the same DNA, so they usually look very similar and are the same sex and blood type in most cases.
  • Fraternal twins share about 50% of their genes, like regular siblings, so they can look quite different and may be a boy–girl pair, two boys, or two girls.

Quick HTML table for your post

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Feature Identical twins Fraternal twins
How they form One fertilized egg splits into two embryos.Two different eggs fertilized by two different sperm.
Genetic similarity Nearly 100% of DNA in common.About 50% of DNA in common, like normal siblings.
Sex Almost always the same sex.Can be same or different sex (boy–girl twins must be fraternal).
Physical similarity Usually very similar in looks and growth pattern.May look similar or different; no more alike than other siblings.

Tiny “Quick Scoop” style summary

  • Identical = one egg, one sperm, split in two → almost clone-like siblings.
  • Fraternal = two eggs, two sperm, same pregnancy → “regular siblings” who just happen to share a birthday.

Information gathered from public forums or data available on the internet and portrayed here.