Distribution of principal frequencies. Fast Fourier Transform was used to determine the principal frequencies of different gene expressions. (a) Histogram of principal frequencies obtained from the microarray data set under alternating light and dark cycles . (b) Distribution of principal frequencies from the Toepel et al. data set  under alternating light and dark periods followed by continuous light. The x-axis shows the frequency and the y-axis shows the number of genes.
Elvitigala et al. BMC Genomics 2009 10:226 doi:10.1186/1471-2164-10-226