Figure 1. Clock/Clock females display lengthened and irregular estrous cycles.

A, Representative estrous cycles as measured by vaginal cytology in wildtype (top), Clock/+ (middle), and Clock/Clock (bottom) females. C = cornified, N = nucleated, L = leukocytic. B, Clock/Clock females have significantly more days of cornified smears compared to wildtype females, as determined by an unpaired t-test for the number of consecutive days cornified (* indicates p < 0.05, ** indicates p < 0.01).