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I understand how cell differentiation works in general (gradients of homeobox proteins etc), but how is timing controlled? Why do some genes switch on at a very specific moment of development and then switch off. I imagine that the timing could be enabled by the same homeobox proteins (genes are switched on as soon as the proteins diffuse far enough, and switched off as soon as the homeobox is used up), but perhaps there's some special mechanism of gene expression timing?

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closed as too broad by Bryan Krause, David, The Last Word, AliceD Oct 24 '18 at 20:40

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ I feel like answering this question would require more than one textbook on developmental biology. Maybe you could narrow it down to a particular event? $\endgroup$ – Bryan Krause Oct 15 '18 at 22:47
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    $\begingroup$ It's controlled by the expression of other genes, the environment and/or maternal effect. You might be interested in this answer. $\endgroup$ – canadianer Oct 16 '18 at 19:29
  • $\begingroup$ @BryanKrause, well, I am mostly interested in how it's generally possible rather than particular cases. Say, a cluster of undifferentiated cells initiates differentiation. Half of the cells assume the fate A, and the rest assume fate B: they undergo very different steps of differentiation and transcribe entirely different proteins. And yet, in 24 hours, they all end up differentiated and forming a functional structure. How are the two completely different pathways could be synchronized so perfectly that they finish at around the same time despite having nothing in common? $\endgroup$ – A.V. Arno Oct 17 '18 at 11:05
  • $\begingroup$ @Anton Did you check out the answer that canadianer linked? I think something like that is going to be about all someone can say. I also think your conception about them "finishing at around the same time" is a bit off, there's no reason that cells have to be "done differentiating" at the same time in terms of all the maturation that goes on. Often the first steps are separating different types of stem cells which go on to differentiate in potentially multiple other separate paths, and for many tissues this never stops during the lifetime. $\endgroup$ – Bryan Krause Oct 17 '18 at 15:31
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How can gene expression timing affect the formation of a developing embryo?

We should know that genetic imprinting is passed down. The formation of an embryo is not. Some takes on form when provoked, it is much like when oocytes are stimulated with a prod duplication Happens automatically. The embryo is affected by the proximity of cells. Clusters, spread out, far apart. All make the cells behave automatically. But it's the first ignition of development that sets off growth. The cells have been through many phases and timing is not controlled by either proteins or genes.

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  • $\begingroup$ Does this not answer your question? $\endgroup$ – Mila sheehan Oct 17 '18 at 22:05

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