Influence On Monozygotic Twins
Identical twins have identical genomes in the immediate aftermath of twinning. Two-thirds of monozygotic twins share the same placenta, arising by cleavage before the fourth day of development; the other third have separate placentas because cleavage has taken place after the fourth day after choriogenesis has begun.
Placentas vary with respect to the transport of nutrients and hormones, a variance that may influence epigenesis. For example, the pattern of X chromosome inactivation is affected by placental status. There is some evidence that it affects the variance in IQ test findings among identical twins, that is, monochorionic identical twins display less IQ variance one from another than do dichorionic identical twins. There is weak evidence that monozygotic twins sharing a placenta have a higher concordance rate for schizophrenia than monozygotic twins with separate placentas. Sharing a placenta increases the risk for infection, and infection in pregnancy has been shown to be a risk factor for schizophrenia. Equally striking is evidence for increasing difference in genomic expression between identical twins as they are once again implicating environmental intercession.
Read more about this topic: Choriogenesis
Famous quotes containing the words influence on, influence and/or twins:
“Books, the oldest and the best, stand naturally and rightfully on the shelves of every cottage. They have no cause of their own to plead, but while they enlighten and sustain the reader his common sense will not refuse them. Their authors are a natural and irresistible aristocracy in every society, and, more than kings or emperors, exert an influence on mankind.”
—Henry David Thoreau (1817–1862)
“Somewhere along the line of development we discover who we really are, and then we make our real decision for which we are responsible. Make that decision primarily for yourself because you can never really live anyone else’s life not even your child’s. The influence you exert is through your own life and what you become yourself.”
—Eleanor Roosevelt (1884–1962)
“What strikes many twin researchers now is not how much identical twins are alike, but rather how different they are, given the same genetic makeup....Multiples don’t walk around in lockstep, talking in unison, thinking identical thoughts. The bond for normal twins, whether they are identical or fraternal, is based on how they, as individuals who are keenly aware of the differences between them, learn to relate to one another.”
—Pamela Patrick Novotny (20th century)