Twin Inheritance: Do Twins Have Twins? Identical vs. Fraternal Genetics

Identical (monozygotic) twins: Random embryo split—not genetic. Having identical twins does not increase your children's twinning chances.

Fraternal (dizygotic) twins: Two eggs fertilized by two sperm. Genetic component exists:

• Heritability: Family history of fraternal twins increases likelihood.
• Shared genes: Variants affecting ovulation/fertility can promote multiple egg release.

Maternal age, environment, and reproductive tech also influence fraternal twinning. Genetics alone don't determine it.