Cloned cats and new statistical laws?

Author: Michael Chernick

The world's first cloned sheep, Dolly, now a stuffed exhibit in the National Museums of Scotland, Edinburgh

The world's first cloned sheep, Dolly,

now a stuffed exhibit in the National

Museums of Scotland, Edinburgh.

Image by Mike Pennington/Wikimedia.

In the December 2010 issue of Science Daily one article (entitled Why a Cloned Cat Isn't Exactly Like the Original: New Statistical Law for Cell Differentiation) talks about the genetics of identical twins and how they differ even though their chromosomes and genetic makeup start out identical. Statistics plays a role in this story but I would hardly call it a new law of statistics.

The story starts out as follows: "Why does a cloned cat look different from the original? A new answer to that question has been found by researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw. Using computer simulations and theoretical calculations they discovered a new statistical law." The author then goes on to explain "Under certain conditions, a population of reproducing cells can spontaneously divide into two groups with distinctly different functions. The researchers have since long been looking for the reasons of such a spectacular process but the mechanisms found so far were complicated and did not explain all observed cases." However, very recently in Warsaw, at the Institute of Physical Chemistry of the Polish Academy of Science, the scientists carried out simulations based on a probabilistic model that seem to explain the cell differentiation.

In an interview Dr Anna Ochab-Marcinek of the Institute stated "We discovered a statistical law that is responsible for cell differentiation." But what is she really talking about?

What goes on is as follows: the genetic information in cells is contained in the animal's DNA structure. The proteins, however, are synthesized based on the sequences in the messenger RNA (mRNA). To produce a protein encoded in a gene, the information must first be transferred from DNA to mRNA. The transfer process (transcription) is controlled by molecules called transcription factors. After attachment to DNA, these molecules may repress (then they are called repressors) or promote (activators) the gene translation. "A cell is a bag with a plenty of various molecules, moving randomly due to thermal motions. So, it may happen that after cell division, one daughter cell will include more transcription factors than the other," Dr. Ochab-Marcinek says. Using computer simulations, the researchers analyzed how a different number of repressors or activators affect the cell population.

What she is calling a "statistical law" is simply the random motion of the molecules. This randomness allows the daughter cells in one twin (clone) to be different than the daughter cells in the other. This explains differences in twins or clones as they develop and also explains why the rest of us look so different in spite of the fact that our genomes are strikingly similar. Quantum mechanics is based on a theory of randomness as it occurs in individual atoms. But we do not call it a law of statistics. No, what we should say here is that this is a new biological law based on a random mechanism. This theory refutes the notion that we are determined strictly by our genes (so-called genetic determinism).

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