Comparisons of three round-amplified products starting with very small quantities of RNA. (a-c) Amplification biases in the products starting from a small quantity of RNA. Scatter plots of signal intensity obtained from 5 μg of BMMC RNA prepared by the standard protocol and from 30 pg (a), 10 pg (b) and 2 pg (c) of BMMC RNA prepared by three rounds of amplification are shown. (d, e) Reproducibility of the three-round amplification of a small quantity of RNA. Scatter plots of signal intensity between two independent products from 30 pg of BMMC RNA (BMMC 30 pg-1 and BMMC 30 pg-2) (d) or from 2 pg of BMMC RNA (BMMC 2 pg-1 and BMMC 2 pg-2) (e), are shown. Red dots show probe sets judged as "Presence", and yellow dots represent probe sets judged as "Absence" in both arrays. Blue dots show probe sets judged as "Presence" only in either array. The correlation coefficients (r) are presented. The same, four-fold induction and suppression thresholds are indicated as diagonal lines. Genes judged as "Presence" are placed in groups corresponding to pairwise overlaps shown in the accompanying Venn diagrams.