Experimental Data

This file is used to determine the background intensity distribution.
It was drawn from the files {11_27_03.cel, 11_27_05.cel, 09_21_04.cel} using this key for background tags.
Intensities <3000 are kept for the distribution.

Fitness scores are calculated by comparing the tag intensities for a strain measured under a perturbation condition to the intensity distributions for each of those tags estimated from replicates of a standard condition. The scores are a measure of the likelihood of observing the experimental condition measurements by given the estimated standard distribution. Thus, a fitness defect score of 100 under a given condition implies that the tag intensities would not likely be seen in many replicates of the control experiments. However, the score does not reveal whether the tags are more or less intense than expected in the standard. This is directly determined by comparison of the measured intensities to the estimated mean of the tag intensities from the standard replicates. Those strains whose tag intensities fall lower than the mean (implying they were dropping out of the population) are classified as sensitive to treatment and those strains whose tag intensities fall higher than the mean are classified as refractory to treatment. Though it seems relatively straitforward to understand the meaning of a significant sensitive score (the strain grows slower in the perturbed condition than in the standard), the significant refractory strains are often harder to explain. Experimentally, many of the strains that turn up as significantly refractory are slow growers. These strains have tag intensity distributions that are not much above background and are therefore unreliable. Although true resistant strains exist in these lists, they are likely to be only a small percentage of the total number of refractory strains.