The two parts of the Atlantic Ocean are clearly divided along equator. The central point can be defined, because the Atlantic is exactly 60° wide along equator from Amazon Esturary to the West Coast of Africa. The equatorial part of the Mid-Atlantic Ridge then reaches equadistant to east and west, accurately 9° to each direction. That is equavalent to 6 convection rolls, as each convection roll spans 1.5° from east to west.
The two ridges are then formed differently, one following the main swaying trend of convection rolls (North Atlantic) and the other follows the NS-trend of the convection rolls system (South Atlantic). Similar difference can be observed on small scale in Iceland, where in the southern half of Iceland the alignment is NE-SW, and then shifts to NS-alignment in the northern half. In turn, we have to analyze why nature makes these ´different choices´, and likewise we should try to explain why we find symmetry of nature as shown here.
The large scale convection rolls of lower mantle are not drawn here. They span 30° from east to west, so the thin yellow line represents the pair of lower mantle convection rolls along equator.