(A) Morphologies of smyhc1+/+, smyhc1-/+ and smyhc1-/- embryos are grossly normal at 2 days post fertilization (dpf), despite complete paralysis of smyhc1-/- embryos. In contrast, the smyhc1R673H/+ embryos have notochord kinks in larval stages (arrow head), while smyhc1R673H/R673H embryos have much more severe notochord kinks that compress and distort the body axis (arrow heads). The smyhc1R673H/- embryos completely phenocopy smyhc1R673H/R673H embryos. (B) Quantification of smyhc1R673H embryonic phenotypes at 2 dpf. 