DNA----transcription----RNA----translation---Protein

One gene - one protein  ( for now)

tissue to tissue variation, time to time variation, subject to subject variation

what is measured ?  goal : the number of mRNA  molecules for each gene (or squence tag) in the sample cells
    Image data :  use laser scanner to obtain  light intensity  at each pixel location
    Eventually converted  and  "treated"  as a measure of abundance of mRNA  ( in a relative sense)

Example :

Yeast Diauxic shift micro-array data (see science article)

Ribosomal proteins

Aging genes affymetrics data (see science article)

What is microarray ?  http://www.nhgri.nih.gov/DIR/LCG/15K/HTML/aboutmicro.html