…John Flaherty, writing in the Arizona Republic (March 28, 2007), revealed that it is no longer a choice between identical and fraternal.
…Vivienne Souter, MD, a doctor at Banner Good Samaritan Medical Center in Phoenix, is lead researcher on the project. The semi-identical twin, she says, is vanishingly rare and used to be considered only a theoretical possibility.
…One in every 32 births is twins. Fraternal twins (two eggs, two sperm) occur once in every 60 births. Identical twins (one egg, one sperm, split in two) once in every 150 births.
…Semi-identical twins can come about from one egg, fertilized by two sperm, then split.
…Or…A single egg splits, then two sperm fertilize each half.
…Academic curiosity or something significant that has been overlooked until now? The docs aren’t sure.
…The twins being studied have abnormalities. One is male, the other a hermaphrodite (both ovarian and testicular tissue). They are also chimeric—meaning they carry two genetic blueprints.
…The toddlers are healthy and happy, the doctors report.
…Souter, the twin investigator, gave birth to twins four years ago. Destiny!