Twins: still 1 sperm per egg
Monozygotic (monoovular):
- A fertilized, single egg splits into two developing zygotes at a very early stage.
- Identical twins; same sex.
Dizygotic (polyovular):
- Result from the fertilization by two sperm of two separate ova that have reached maturation at the same time.
- Not identical twins; can be different sexes
- Incidence increases with age of the mother