Choriogenesis

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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. [1]

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Influence on monozygotic twins

Identical twins have identical genomes in the immediate aftermath of twinning. About 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. [2]

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 a weak link between variance in IQ test findings and chorion type. A study in 1978 shows that white monochorionic identical twins display less IQ variance one from another than do white dichorionic identical twins, although similar results could not be repeated with black twins. [3] 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.

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Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their genetic inheritance (nature) and the environmental conditions of their development (nurture). The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French. The complementary combination of the two concepts is an ancient concept. Nature is what people think of as pre-wiring and is influenced by genetic inheritance and other biological factors. Nurture is generally taken as the influence of external factors after conception e.g. the product of exposure, experience and learning on an individual.

<span class="mw-page-title-main">Placenta</span> Organ that connects the fetus to the uterine wall

The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ, producing hormones that regulate both maternal and fetal physiology during pregnancy. The placenta connects to the fetus via the umbilical cord, and on the opposite aspect to the maternal uterus in a species-dependent manner. In humans, a thin layer of maternal decidual (endometrial) tissue comes away with the placenta when it is expelled from the uterus following birth. Placentas are a defining characteristic of placental mammals, but are also found in marsupials and some non-mammals with varying levels of development.

<span class="mw-page-title-main">Twin</span> One of two offspring produced by the same pregnancy

Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic, meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell. Since identical twins develop from one zygote, they will share the same sex, while fraternal twins may or may not. In very rare cases fraternal twins can have the same mother and different fathers.

<span class="mw-page-title-main">Heritability</span> Estimation of effect of genetic variation on phenotypic variation of a trait

Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"

Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.

<span class="mw-page-title-main">Chorion</span> Outermost fetal membrane around the embryo in amniotes

The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It is also present around the embryo of other animals, like insects and molluscs.

<span class="mw-page-title-main">Heritability of autism</span> The rate at which autism is inherited

The heritability of autism is the proportion of differences in expression of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic. Autism has a strong genetic basis. Although the genetics of autism are complex, autism spectrum disorder (ASD) is explained more by multigene effects than by rare mutations with large effects.

<span class="mw-page-title-main">Placentation</span> Formation and structure of the placenta

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<span class="mw-page-title-main">Syncytin-1</span> Protein found in humans

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In multivariate quantitative genetics, a genetic correlation is the proportion of variance that two traits share due to genetic causes, the correlation between the genetic influences on a trait and the genetic influences on a different trait estimating the degree of pleiotropy or causal overlap. A genetic correlation of 0 implies that the genetic effects on one trait are independent of the other, while a correlation of 1 implies that all of the genetic influences on the two traits are identical. The bivariate genetic correlation can be generalized to inferring genetic latent variable factors across > 2 traits using factor analysis. Genetic correlation models were introduced into behavioral genetics in the 1970s–1980s.

<span class="mw-page-title-main">Monochorionic twins</span> Identical twins that share the same placenta

Monochorionic twins are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins, these are monochorionic multiples. Monochorionic twins occur in 0.3% of all pregnancies. Seventy-five percent of monozygotic twin pregnancies are monochorionic; the remaining 25% are dichorionic diamniotic. If the placenta divides, this takes place before the third day after fertilization.

<span class="mw-page-title-main">Zygosity</span> Degree of similarity of the alleles in an organism

Zygosity is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.

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<span class="mw-page-title-main">Fetal membranes</span> Amnion and chorion which surround and protect a developing fetus

The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals. They are the amnion, chorion, allantois, and yolk sac. The amnion and the chorion are the chorioamniotic membranes that make up the amniotic sac which surrounds and protects the embryo. The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord.

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The genetic mechanism of synesthesia has long been debated, with researchers previously claiming it was a single X-linked trait due to seemingly higher prevalence in women and no evidence of male-male transmission This is where the only synesthetic parent is male and the male child has synesthesia, meaning that the trait cannot be solely linked to the X chromosome.

Personality traits are patterns of thoughts, feelings and behaviors that reflect the tendency to respond in certain ways under certain circumstances.

References

  1. Glanze, Walter D.; Anderson, Kenneth; Anderson, Lois E. (1992). "Choriogenesis". The Mosby Medical Encyclopedia . New York: Plume. ISBN   0-452-26672-6.
  2. Marceau, Kristine; McMaster, Minni T. B.; Smith, Taylor F.; Daams, Joost G.; van Beijsterveldt, Catharina E. M.; Boomsma, Dorret I.; Knopik, Valerie S. (2016). "The Prenatal Environment in Twin Studies: A Review on Chorionicity". Behavior Genetics. 46 (3): 286–303. doi:10.1007/s10519-016-9782-6. ISSN   0001-8244. PMC   4858569 . PMID   26944881.
  3. Melnick, M; Myrianthopoulos, N C; Christian, J C (July 1978). "The effects of chorion type on variation in IQ in the NCPP twin population". American Journal of Human Genetics. 30 (4): 425–433. ISSN   0002-9297. PMC   1685620 . PMID   568880.