(a) Northern blot analysis of CS2KO9 and CS2KO consecutively probed with IT4var 19 and var exon two sequences (exon2). (b) Quantities of different var gene transcripts in BeWo selected CS2KO9 and unselected CS2KO parasites. Absolute quantification of var gene transcripts was performed by quantitative RT-PCR using standard curves of plasmids containing the var gene target sequences. Presented data is normalized against 18S rRNA levels so that molecules of var cDNA from equivalent numbers of cells for each parasite line are compared. Data are presented as mean + standard deviation.