Table 1. Alleles of previously characterized genes.

Mutant	Phenotype	Gene	Mutation	Nature of allele
bent body (bnb)	Dorsalized spinal cord, left-right randomization, die at e9.0	Smo (19)	Splice site	Null
2A	Dorsalized spinal cord, left-right randomization, die at e9.0	Kif3a	Not determined	Null
flexo (fxo)	Abnormal diencephalon, no floor plate in caudal spinal cord, left-right randomization, polydactyly, die at e13-14	Polaris (13)	Splice site	Hypomorph
M1un	Arrested unturned, variable cardia bifida; arrest at e9.0	Pten	Missense (M134K)	Hypomorph
DD1	Caudal paraxial mesoderm replaced by neural tubes	Tbx6	Splice site	Null