  Experiments have shown that during the initial stage of Zebrafish
morphogenesis a synchronous to asynchronous transition (SAT) occurs, as the
cells divide extremely rapidly. In the synchronous phase, the cells divide in
unison unlike in the asynchronous phase. Despite the widespread observation of
SAT in experiments, a theory to calculate the critical number of cell cycles,
$n^{*}$, at which asynchronous growth emerges does not exist. Here, using a
model for the cell cycle, with the assumption that cell division times are
Gaussian distributed with broadening, we predict $n^{*}$ and the time at which
the SAT occurs. The theoretical results are in excellent agreement with
experiments. The theory, supplemented by agent based simulations, establish
that the SAT emerges as a consequence of biomechanical feedback on cell
division. The emergence of asynchronous phase is due to linearly increasing
fluctuations in the cell cycle times with each round of cell division. We also
make several testable predictions, which would further shed light on the role
of biomechanical feedback on the growth of multicellular systems.
