by Marc Abrahams
In the early 1960s, a fellow named
Sonneborn
discovered a big peculiarity in a tiny animal, the paramecium.
Sonneborn would take a paramecium, and disfigure it. Later, after the
paramecium reproduced itself, its children (and their descendants, too!)
inherited that same disfiguration. That inheritance raises a question
that should disturb and intrigue every living biologist: How was the
information — the location and shape of the disfiguration — passed from
one generation to the next?
About Paramecia, and About Inheritance
First, a little background about paramecia.
A paramecium is a one-celled creature. It has a distinctive shape,
rather like that of a slipper; it’s the shape you see repeated on a
paisley tie. The paramecium is a ciliate, which is to say that its
surface has lots of little, whip-like projections called cilia. The
cilia are generally arranged in parallel rows, and within the rows, each
cilium has pretty much the same orientation. (This is analogous to the
hairs on a patch of your skin — on a small patch the hairs all point in
the same direction). The cilia wag back and forth rather like floppy
oars. This concerted wagging is how the animal moves itself about.
Second,
a little background about how shape and other information is passed on
from generation to generation. Every living thing has received from its
parent (or parents) the set of instructions necessary to physically live
and grow. Those instructions are carried, in tickertape fashion, in the
genes. The genes are made entirely of deoxyribonucleic acid (the famous
DNA), arranged as long, long, astoundingly thin, twisty, scrunched-up
tickertape-like molecules. All of modern biology is based on this idea —
that virtually all the physical information that’s passed from parent
to child is contained in the DNA. In a paramecium, the most famous
chunks of DNA are contained in the nucleus. Some other parts of the cell
also contain their own little chunks of DNA.
What Sonneborn Found
With that background in mind, consider what Sonneborn found, and how puzzling his discovery is.
Tracy M. Sonneborn was an Indiana University biologist, known and much respected for doing careful research. His
paramecia experiments,
in particular, are carefully documented. In these experiments,
Sonneborn would slice off a little chunk of a paramecium’s surface, then
rotate the slice and plop it back on. It was easy to see where the
grafted slice now lay. Its rows didn’t line up with the neighboring
rows, and the individual cilia were oriented in the “wrong direction”
compared to cilia in the neighboring, undisturbed rows. And because its
cilia in the altered patch were wagging in a different direction from
that of their neighbors, the altered paramecium would, typically, move
in some mildly eccentric way.
The startling thing is what happened after the paramecium reproduced.
For a paramecium, reproduction is usually a lonely, mitotic affair. The
thing just splits itself in two.
Each offspring of a maimed paramecium turned out to have the same
graft pattern as its parent, with the rotated patch of cilia in the
same, odd orientation. This flipping of the paramecium’s wig makes
biologists flip their own wigs, those few who have heard about it.
It’s hard, very hard, to see how this could possibly be inherited via
the genes. Yet somehow the information is passed on from the paramecium
that got the disfiguration to its children, and on to subsequent
generations. How? How?
Where Might This Lead?
Sonneborn died in 1981. Nary a soul has picked up on his work and
tried to see where the big question might lead. Maybe it leads nowhere,
maybe it leads somewhere very, very interesting. Perhaps you, or someone
you know, will be the person who discovers the answer to this question.
Where to Start
If you want to dig into Sonneborn’s work, a good place to start is
one of his reports: “Cytoplasmic Inheritance of the Organization of the
Cell Cortex in Paramecium Aurelia,” Janine Beisson and T.M. Sonneborn,
Proceedings of the National Academy of Sciences, vol. 53, no. 2, February 1965, pp. 275-82. Good luck. If you do some experiments and find an answer, please let us know.
Poor
bees. First, there's the honeybee colonies
collapse disorder, then there's this: a parasite that turns bees into
zombies.
