FlyBase curator comment: this entry is used to capture phenotypic information when the particular allele (or allele combination) used by the author could not be determined but the context of the experiment suggests that the phenotype being described is some kind of loss of function.
When mutant germ cells are transplanted into embryos without germ cells (tud mutants) they exhibit migration defects. When wild-type germ cells are transplanted into mutant embryos they migrate normally.