sentence: The genes broadly fell into three categories , those least abundant genes with mean C values of 27-32 ( SLC25A23 , MRPL19 , DTX3 and CHRNB4 ) , moderately abundant genes with mean C values of 22-26 ( HPRT and ACTB ) and the most abundant highly expressed genes with mean C values of 19-21 ( B2M , PPIA and GAPDH ) Table 2 .