Gene expression

To complicate the situation, just because a gene is present does not mean that that it is necessarily transcribed and translated (expressed) all the time. The monitoring of when, where, and how a gene is expressed is commonly referred to as expression profiling.

So, genomics and comparative genomics can involve studying the location of genes, changes in their sequence (such as in evolutionary studies) and how they are expressed.

Millet, healthy (l) and diseased with downy mildew (r).

Once the pattern of gene expression under normal circumstances is known, one can then study what happens when the plant is affected by disease or stress, or how expression varies as the plant ages.