Random determination of a developmental process: reversal of normal visceral asymmetry in the mouse.

Situs inversus viscerum in the mouse has been shown to be inherited as an autosomal recessive trait (gene symbol iv) with reduced penetrance. It is hypothesized that the normal allele at the iv locus exhibits complete dominance and controls normal visceral asymmetry. Absence of this control allows the situs of visceral asymmetry to be determined in a random fashion. This hypothesis also appears to apply to the inheritance of situs inversus in man and to the experimental production of situs inversus.