Decrease in the number of CL in ovaries of MC4R-/- mice. The number of CL was determined in completely dissected H.E. stained ovaries. Compared with MC4R+/+ mice the number of CL is significantly lower in MC4R-/- mice at a mixed C3H/B6 (1st cohort) and at a B6 background (2nd cohort). A: The difference in the 1st cohort appears to increase with animal age in months. B: shows the data broken down into animals with vaginal signs of estrus and metestrus. Data are presented as box-and-whisker plots with median (line), interquartile range (box), minimum and maximum range (whisker) and outliers (cross); n indicates the number of animals; * indicates significant differences with p value ≤ 0.05.