Gene expression, assessing levels

The vast majority of the smdies on antibiotic resistance in the environment have focussed on the survey of resistance genes. However, the mere detection of the antibiotic resistance genes may be insufficient to get a clear perspective of their function in the environment. If the role of antibiotic resistance genes in the environment is to be assessed, it is also important to determine the factors capable of triggering gene expression and to measure the expression levels [24]. Such an approach requires transcriptomic analyses supported, for instance, by reverse-transcription PCR or microarrays. 

Another important point was made by this study if possible, use reference samples with gene expression levels similar to those expected for the test samples. This should improve quantification at the low end. Moreover, the Tan et al., (2003) and Barczak (2003) studies also demonstrate the need for the standardization of commercial microarray products and reference standards so that both interlaboratory and cross-platform performances can be properly assessed. While commercial microarrays from different vendors all claim substantial gene probe "real estate," the number of probes in common is smaller. This makes it difficult to compare experiments across platforms, especially those from major suppliers such as Affymetrix, Agilent, and Amersham (Figure 2.8). 

Toxicogenomics tries to assess the toxicity and safety of chemical compounds by analyzing gene expression changes detected by measuring mRNA levels using DNA microarrays (1,2). 

---