Choriogenesis
Encyclopedia
In developmental biology
, choriogenesis is the formation of the chorion
, an outer membrane of the placenta that eventually forms chorionic villi
that allow the transfer of blood and nutrients from mother to fetus.
s 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.
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
, choriogenesis is the formation of the chorion
Chorion
The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes...
, an outer membrane of the placenta that eventually forms chorionic villi
Chorionic villi
Chorionic villi are villi that sprout from the chorion in order to give a maximum area of contact with the maternal blood.Embryonic blood is carried to the villi by the branches of the umbilical arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the...
that allow the transfer of blood and nutrients from mother to fetus.
Influence on monozygotic twins
Identical twins have identical genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s 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
Epigenesis (biology)
In biology, epigenesis has at least two distinct meanings:* the unfolding development in an organism, and in particular the development of a plant or animal from an egg or spore through a sequence of steps in which cells differentiate and organs form;...
. 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
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
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.