Monday, October 03, 2005

Noise   posted by Fly @ 10/03/2005 08:50:00 AM


“unscripted biochemical variations, or noise, combined with time delays in certain biochemical reactions may lead to oscillations in gene regulation that couldn’t otherwise be predicted. Such noise is routinely described by cell biologists who record large phenotypic differences between supposedly identical cells in a single flask of growth medium.”

“The fine-grain fluctuations we see in the genetic regulation within single cells may lead to new insights about variability at the level of the whole organism”

Noise is under appreciated. Some speculation on noise…

Noise prevents sharp “edge” effects. Imagine a thermostat with no “noise”. Too cold then turn on, too hot then turn off, the heater would be continually turning on and off. Slop in a steering wheel is another example. If the wheel is too responsive then the driver over corrects.

“Noise” in the genome: Mutations generate new gene alleles. If the new allele significantly improves fitness then it rapidly increases in frequency. If the new allele significantly decreases fitness, then it may disappear. But many mutations won’t have much of an effect either way. Such gene alleles act as genetic “noise”. Such genetic noise produces statistical “outliers” that are extreme phenotypes. (E.g., very high IQ.)

Gene allele “outliers” provide feedback. If the environment changes so that the “outlier” significantly improves fitness then that gene allele frequency increases and the population rapidly adapts. Negative “outliers” would “push” the population away from the “bad” allele. Thus noise makes the genome more robust and stable.

Molecular noise provides the random generator needed to for our body’s immune system to build broad coverage against potential invaders and generate new antibodies to specific molecular targets against invaders that make it past the first immune barrier.

Noise can provide the “mutations” in a Darwinian mechanism such as might occur in thinking and skill learning. (Similar to “heat” in simulated annealing.)

Noise keeps certain neuronal systems healthy. Too little noise can lead to heart attacks or seizures.

Update from Razib: Look in the gnxp files for "noise," that is the PDF of the paper that the article is based on.