Genes and Information

Scientific American profiles James Collins, who is a pioneer in the field of “synthetic biology”.

Collins soon led a team that in 1999 created a genetic toggle switch. It consists of two foreign genes, each of which produces a protein that inhibits the other gene. Depending on the chemical added to the bacterial broth, the proteins of one gene would effectively be deactivated, disabling that gene. "The toggle switch is significant because no further modulation is necessary," Cantor says. Conventional genetic engineering needs continual insertion of a stimulant to keep the new gene running. The toggle switch stays on, or off, for as long as the organism remains alive.

The genome may be the Operating System of a cell, but it is pretty useless unless the rest of the cell “boots” it up. From the same issue, this article by Gil Ast is the best explanation (for regular folks) that I have ever seen of how genes actually express themselves within a cell.

Along the same lines, Steven Rose reviews Sean Carrol’s “Endless forms most beautiful” here.

A fertilised egg is not entirely symmetrical. It is marked by the point at which the sperm enters it. From this singularity one can define north and south poles (top and bottom), east and west (right and left). As the cell divides, these geographical markers define the axes of development of the organism. All its daughter cells contain the same genes and regulators, but it is the positional information that ensures which genetic switches are thrown when. Time depends on place, and the emerging structure depends on both.

Finally, how inheritance can sometimes occur even without genes. It appears that the cell in no tabula rasa either- the expression of genes may often depend on the particular cell it finds itself in.

Hmmm....RNA passes into the fertilized egg and silences the activity of a gene? How does this handful of RNA molecules continue to stifle the gene in the descendents of the embryo? Is it by some “tag” that is placed on the genes and is carried along with it? Or does the RNA get the cell to manufacture more copies of itself? If the latter, sounds suspiciously like a retrovirus.