In trh6 homozygous embryos, salivary duct cells fail to invaginate, instead remaining clustered on the surface of the embryo.
The filzkorper do not elongate and trachea do not form properly. The oesophagus, gastric caecae and Malpighian tubules are unaffected.
trh alleles fall into an allelic series. From strongest to weakest: trh1 = trh8 > trh7 > trh10512 > trh6 > trh5 > trh4.