A–Z Glossary

Fraternal twins

Twins that begin as two separate eggs fertilized by two separate sperm, like ordinary siblings.

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Identical vs fraternal twins differences

Identical vs fraternal twins differences

The basic biology behind twin types Twin pregnancy begins in one of two broad ways. In a monozygotic pregnancy, a single egg is fertilized by a single sperm, creating one zygote. That early embryo then splits into two separate embryonic lines, which develop into identical twins. In a dizygotic pregnancy, two eggs are released in […]