Fig. 10. RT-PCR analysis of MyoD expression in different stage embryos developing at different temperatures. At all temperatures, MyoD transcripts are switched on as the somites began to form. Note that despite the lack of in situ staining for MyoD beyond approximately the 35-somite stage (Fig. 10), transcripts are still present. L15 is a 60S ribosomal subunit `housekeeping' gene, expressed at all temperatures and in all stages, used as an internal standard. The positions of marker nucleotides (bp) are shown at left.