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Related Concept Videos

Chirality in Nature02:30

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Chirality is the most intriguing yet essential facet of nature, governing life’s biochemical processes and precision. It can be observed from a snail shell pattern in a macroscopic world to an amino acid, the minutest building block of life. Most of the snails around the world have right-coiled shells because of the intrinsic chirality in their genes. All the amino acids present in the human body exist in an enantiomerically pure state, except for glycine - the sole achiral amino acid.
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Creating Avian Forebrain Chimeras to Assess Facial Development
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Natural human chimeras: A review.

Kamlesh Madan1

  • 1Department of Clinical Genetics, Leiden University Medical Center, Post Box 9600, 2300 RC, Leiden, the Netherlands.

European Journal of Medical Genetics
|June 23, 2020
PubMed
Summary

Human chimeras, organisms with cells from multiple zygotes, can form naturally through fetal-maternal cell exchange or zygote fusion. Many chimeras remain undetected, with potential medical and legal implications.

Area of Science:

  • Genetics
  • Developmental Biology
  • Human Biology

Background:

  • Chimerism, the presence of cells from two or more zygotes within a single organism, has roots in Greek mythology and a significant history in biological research.
  • Natural human chimeras can arise from fetal-maternal cell transfer across the placenta or the fusion of two zygotes during early embryonic development.
  • While artificial chimeras exist in transplant recipients, this review focuses on naturally occurring human chimeras, first identified in 1953.

Purpose of the Study:

  • To review the origins and implications of natural human chimeras.
  • To discuss the various mechanisms by which human chimerism can occur.
  • To highlight the potential medical, social, forensic, and legal consequences of human chimerism.

Main Methods:

Keywords:
Blood chimerasFusion chimerasHuman natural chimerasMicrochimeras

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  • Literature review of reported cases and biological mechanisms of natural human chimerism.
  • Analysis of genetic and phenotypic data from identified human chimeras.
  • Comparison with chimerism observed in other species, such as marmoset monkeys.

Main Results:

  • Natural chimerism can result from fetal-maternal microchimerism or fusion of zygotes, often remaining undetected.
  • Sex-discordant chimeras (e.g., 46,XX/46,XY karyotype) can exhibit normal male or female phenotypes, with intersex conditions being less common than previously assumed.
  • Blood chimerism is relatively common in dizygotic twins due to placental blood exchange, and while germ cell chimerism occurs in marmosets, it has not been documented in humans.

Conclusions:

  • Human chimerism is a complex phenomenon with diverse origins and varying degrees of detection.
  • The prevalence of undetected chimerism may necessitate a re-evaluation of its medical, social, forensic, and legal implications.
  • Further multidisciplinary research is essential for a comprehensive understanding of human chimerism.