Fig. 5. Gene expression in 3.5 dpc ICMs, 4.5 dpc ICMs and ES cells. Amplified cDNA from individual ICMs and single ES cells were mixed according to the genotype and gene expression was assayed by semiquantitative PCR. cDNA made with a conventional method from 1 µg total RNA of ES cells was used to assess the quality of amplified cDNA. The number of PCR cycles for each gene is shown alongside (left for amplified cDNA, right for conventional ES cell cDNA). `(+/?)' indicates embryos of either (+/+) or (+/-) genotype.