(A–D) terra-hybridized chick embryos. Node, presomitic mesoderm (PSM) and somite expression at (A) 2-somite and (B) 14-somite stages. The lines correspond to sections in (C). (C) Transverse sections showing terra expression in PSM (a), dorsal somite (b) and dermomyotome (c). (D) Somites, eye, otic vesicle and tectum expression at st22HH. (E–P) Zebrafish embryos injected with 4.5 ng of morpholino (MO). (E, I, M) Control-MO-injected 6-somite embryos. (E) deltaC, (I) her1 and (M) her7 expression is symmetrical in 80% (n = 20), 76% (n = 21) and 79% (n = 38) and slightly asymmetrical in 20% (n = 20), 14% (n = 21) and 21% (n = 38) (not shown), respectively. her1 expression is asymmetrical in 9% (n = 21) (not shown). (F–H, J–L, N–P) terra-MO1-injected 10-somite embryos. deltaC, her1 and her7 expression is asymmetrical in (F) 46.1% (n = 26), (J) 58.3% (n = 24) and (N) 47% (n = 31), slightly asymmetrical in (G) 23% (n = 26), (K) 17.6% (n = 24) and (O) 25.8% (n = 31) and symmetrical in (H) 30.7% (n = 26), (L) 25% (n = 24) and (P) 29% (n = 31), respectively. Panels show dorsal views, anterior to the top, except in (C) and (D).