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It is difficult to assume that the massive number of co-ordinated developmental sequences in a developing embryo is controlled by molecular signalling alone. Is anyone aware of a molecular or developmental clock within the genome which control the on off states of the genes concerned with developmental sequences? If it has not been reported is it likely to exist? (This is not about the molecular clock in evolution.)

Assuming there is a molecular clock, is it possible that the clock is switched on at the time of fertilization, and the zygote transfers the elapsed time to the progressive generations of the cells?

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You think it is difficult to believe that development is only timed by molecular events, but you are asking whether there is a molecular clock? Seems a bit contradicting... Anyway it has been shown that disruption of clock genes leads to developmental defects: for instance (these are just two random papers I found, but there is surely more) ncbi.nlm.nih.gov/pubmed/22884368 ncbi.nlm.nih.gov/pubmed/17963275 –  nico Aug 13 '13 at 6:55
    
Thanks for the comments Nico, I did not say events, i said molecular signalling and molecular clock. by molecular clock I meant something like a run time clock or a timer for that matter for referance.The circardian rhythm is too slow for temporal refernce control of the fast paced developmental process in an embryo. –  Ram Manohar M Aug 13 '13 at 18:08
    
Ok, now I understand what you mean. In general when speaking about "molecular clock" one refers to a set of genes and their derived proteins that govern circadian rhythms and that indeed act as a "24h timer". See also my explanation here: biology.stackexchange.com/questions/2299/… . Now, although these genes are involved in circadian (~24h) rhythms, they possibly also have a role in shorter (<24h, ultradian) and longer (>24h infradian) rhythms, although this is still very much an unresolved question. –  nico Aug 13 '13 at 19:01
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