  Electronic nematicity is the spontaneous loss of rotational symmetry in a
metal, without breaking translational symmetry. In the cuprate superconductors,
there is experimental evidence for nematicity, but its origin remains unclear.
Here we investigate the onset of nematicity in the transport of charge by means
of electric and thermoelectric measurements in underdoped YBa$_{\rm 2}$Cu$_{\rm
3}$O$_{\rm y}$, performed by passing the current (electrical or thermal) first
along the $a$ axis then the $b$ axis of the orthorhombic structure in the same
crystal, with a hole doping $p = 0.12$. Upon cooling, we observe no additional
in-plane anisotropy -- beyond the background anisotropy due to the CuO chains
-- in either the resistivity $\rho$ or the Seebeck coefficient $S$ as the
temperature $T^{\star}$~for the onset of the pseudogap phase is crossed. We
conclude that the pseudogap phase of cuprates is not nematic. However, at
temperatures much lower than $T^{\star}$, a strong additional anisotropy is
observed, most clearly in the Peltier coefficient $\alpha = S / \rho$. We
interpret it as nematicity associated with the development of charge order.
