D (A) (B) Questions 1. How can relative levels of expression in the retinas of 1-day-old and 28-day-old mice be determined in this experiment? 2. What conclusions can be drawn from observations of spots A, B, C, and D?

Experiment A microarray was hybridized with a mixture of two differentially labeled fluorescent cDNAs, one prepared using retinal RNA of 1-day-old mice (labeled with a green fluorescent dye) and the other prepared using retinal RNA of 28-day-old mice (red fluorescence). The two probes were prepared from identical amounts of retinal tissues and were mixed together for hybridization to the microarray. Unhybridized probes were washed away, and the microarray was photographed in a fluorescence microscope.