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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

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The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive March 13, 2014

 

Turing's theory underlies pattern formation in every biological area from
pigmentation of seashells to the shapes of flowers and leaves —
to the geometric structures seen in drug-induced hallucinations.


Image Credit: Wikimedia.org.






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How a zebra gets its stripes

Research from the University of Pittsburgh and Brandeis University proves Alan Turing’s Theory of Morphogenesis 60 years after his death.

British mathematician Alan Turing is known for his computer science — he cracked the code of the German Enigma machine which encrypted Germany's war secrets during World War II, ending the war. But, he also had a tremendous impact on biology and chemistry. In his only paper in biology, Turing proposed a theory of morphogenesis, or how identical copies of a single cell differentiate from a single uniform state — a cell — into an organism with arms, legs, head and tail.

Writing in 1952, before the discovery of the double helix structure of DNA by James D.Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin, Turing wrote "The Chemical Basis of Morphogenesis" describing how non-uniformity (stripes, spots, spirals, etc.) may arise naturally from a uniform state of being. The theory has served as a basic model in theoretical biology, and is seen by some as the very beginning of chaos theory.

Now, 60 years after Turing’s death, researchers from the University of Pittsburgh and Brandeis University provide the first experimental evidence validating Turing’s theory in cell-like structures. The team published their findings in the Proceedings of the National Academy of Sciences on March 10, 2014.


In 1952, Turing was the first to offer an explanation of morphogenesis through chemistry.

He theorized that identical biological cells differentiate and change shape through a process called intercellular reaction-diffusion.

In his model, chemicals react with each other and diffuse across space — or between cells in an embryo.


These chemical reactions are managed by the interaction of agents that either inhibit or excite the process. When this interaction plays out in an embryo, it creates patterns of chemically different cells. Turing predicted six different patterns could arise from his model.

The researchers observed all six patterns predicted by Turing — plus a seventh unpredicted by Turing.

They noticed, as Turing believed in the 1950s, that once identical cell-like structures became chemically different — they also began to change in size due to osmosis. Osmosis, the process of molecules moving through a membrane to maintain balance on either side of that membrane, is affected by changes in temperature. This may explain why some cells, further down the development assembly line, become large egg cells while others become tiny sperm cells.


The research “tells you how a zebra gets its stripes,” says Ermentrout. Turing's theory underlies pattern formation in every biological area from pigmentation of seashells to the shapes of flowers and leaves — to the geometric structures seen in drug-induced hallucinations.

Validating Turing’s theory could have an impact on future research in fields ranging from embryology to neurology to cardiology.


The research could impact not only the study of biological development but the study of materials science as well. For example, Turing’s model could help grow soft robots with predictable patterns and shapes.

Significance
Turing proposed that intercellular reaction-diffusion of molecules is responsible for morphogenesis. The impact of this paradigm has been profound. We exploit an abiological experimental system of emulsion drops containing the Belousov–Zhabotinsky reactants ideally suited to test Turing’s theory. Our experiments verify Turing’s thesis of the chemical basis of morphogenesis and reveal a pattern, not previously predicted by theory, which we explain by extending Turing’s model to include heterogeneity. Quantitative experimental results obtained using this artificial cellular system establish the strengths and weaknesses of the Turing model, applicable to biology and materials science alike, and pinpoint which directions are required for improvement.

Abstract
Alan Turing, in “The Chemical Basis of Morphogenesis” [Turing AM (1952) Philos Trans R Soc Lond 237(641):37–72], described how, in circular arrays of identical biological cells, diffusion can interact with chemical reactions to generate up to six periodic spatiotemporal chemical structures. Turing proposed that one of these structures, a stationary pattern with a chemically determined wavelength, is responsible for differentiation. We quantitatively test Turing’s ideas in a cellular chemical system consisting of an emulsion of aqueous droplets containing the Belousov–Zhabotinsky oscillatory chemical reactants, dispersed in oil, and demonstrate that reaction-diffusion processes lead to chemical differentiation, which drives physical morphogenesis in chemical cells. We observe five of the six structures predicted by Turing. In 2D hexagonal arrays, a seventh structure emerges, incompatible with Turing’s original model, which we explain by modifying the theory to include heterogeneity.

Authors
Nathan Tompkins, Ning Li, Camille Girabawe, Michael Heymann, G. Bard Ermentrout, Irving R. Epstein, and Seth Fraden

The research was funded in part by grants from the National Science Foundation Material Research Science and Engineering Center (DM-0820492 and CHE-1012428). Nathan Tompkins, Ning Li, Camille Girabawe, and Michael Heymann, all from Brandeis University, also contributed to the paper, titled “Testing Turing’s theory of morphogenesis in chemical cells.”