Tracy Sonneborn - Non-Mendelian Inheritance

Non-Mendelian Inheritance

In the late 1950s he conducted an elegant series of experiments in his endeavours to discover what it is that mediates the synchronised movement of the paramecium's cilia. These minuscule hair-like projections enable the cell to 'swim'. They move together and paddle the cell through the water in which it lives.

The paramecium is a single-cell organism, so has nothing remotely resembling a brain. Yet its cilia move together like dancers in a ballet. How is it that their movements are co-ordinated?

Sonneborn surgically removed a small section of cell wall and replaced it rotated by 180 degrees. The cilia in the replaced section continued to 'wave' in the same direction as they had before surgery, i.e. now in antiphase to the others. What was remarkable is that both daughters of paramecia on which this operation had been performed also showed the same trait of a reverse phase wave in a similar area of their cell wall, as did, to a lesser extent, the granddaughter cells.

It is a mark of his excellence as a scientist that he should have taken the trouble to follow the fate of subsequent generations and so be able to make this observation. It may seem surprising that the clear evidence for non-Mendelian inheritance should have been largely overlooked by the scientific community. Further research was at that time limited because the available staining techniques to allow electron microscopy denatured the microtubules which 'power' the cilia so their presence in cells could not be seen. It may also be that, as at that time the mechanisms of genetic inheritance in DNA were becoming open to investigation, this example of non-Mendelian inheritance was not of great interest to the scientific community.