This homozygous lethal allele originated in a mouse caught in the New York suburbs. It suppresses recombination and is a member of the complementation group: t^w5 ,t^w6 ,t^w10 ,t^w11 ,t^w13 ,t^w14 ,t^w15 ,t^w16 ,t^w17 ,t^w37 , t^w38 ,t^w39 ,t^w41 ,t^w46 ,t^w47 ,t^w74 ,t^w75 ,t^w80 ,t^w81. T/t^w5 phenotype is tail-less.

Embryos homozygous for t^w5 arrest at gastrulation and exhibit defects in proliferation/differentiation of embryonic ectoderm.