Fig. 7. Frequencies of seminiferous tubules at indicated stages and of apoptotic tubules (red bar) in B6 (white bars) and Rb/+ (black bars) adult mice. Sectioned material was staged with Periodic Acid-Schiff reagent and Hematoxylin, and processed using the TUNEL method for detecting apoptotic cells. All stage XII tubules in Rb/+ mice were apoptotic (red). Asterisks represent paired values that differ significantly (Student's t test; P=0.035 for difference in frequency of stage VII-IX tubules and P=0.033 for difference in frequency of stage XII tubules).