Fig. 1

Characteristics of the study populations used and number of age-CpGs identified. Age distributions in the datasets are also visualized as histograms in Additional file 5: Fig. S1. Notably, the number of age-CpGs identified in each dataset was associated with the age range in the dataset. The data sets are shown in ranked order according the age interquartile range (IQR). Number of identified age-CpGs in each data set in males and females and in X (A) and Y chromosome (B) is visualized as bars. The number was higher in the X chromosome, as compared to the Y chromosome, reflecting the number of probes available for each chromosome on the Illumina 450 K array (11648 X chromosomal probes, 416 Y chromosomal probes). n = number of individuals in the data set