<p>Bilateral optimal <i>Tbx5</i> expression reaches above a threshold level that buffers the inherent asymmetry in the left and right LPM, which includes the future forelimb-forming regions. Bilateral, suboptimal <i>Tbx5</i> expression levels that fail to reach threshold levels leads to abnormalities in limb formation and cannot buffer the inherent asymmetry in the LPM and as a result the left limb is more severely affected by lowered Tbx5 activity than the right limb.</p
