Germ cells fail to migrate and do not reach the gonad in embryos lacking maternal and zygotic Tre1 function (derived from homozygous females mated to hemizygous males). Homozygous embryos derived from females containing one copy of Tre1[+] do not show defects in germ cell migration. One paternally derived copy of Tre1[+] is also sufficient to rescue the germ cell migration defect of embryos derived from homozygous females, although these embryos have a defect in germ cell death, containing on average 7.0 germ cells ectopic to the gonads compared to 0.5 germ cells ectopic to the gonads in wild-type embryos.

Eggs laid by mutant mothers have a strong germ cell transgut migration defect.

97.8% of embryos derived from homozygous females mated to homozygous males show defects in germ cell migration; germ cell development appears to be normal prior to migration, but very few germ cells, if any, successfully migrate to and become incorporated into the gonad. The germ cells instead become dispersed throughout the posterior half of the embryo and continue to express a germ cell marker (indicating a failure in cell death). The mutant germ cell phenotype is recessive and a maternal effect (it is only seen in the offspring of homozygous females). When homozygous Tre1^sctt females are mated to wild-type males, embryos of two classes are produced. The first class (60% of the embryos) shows the severe germ cell migration defect seen in the progeny of homozygous females mated to homozygous males and germ cells outside the gonad continue to express the germ cell marker. In the second class, an increased number of germ cells successfully migrate to the gonad, but many cells outside of the gonad continue to express the germ cell marker. This less severe class represents embryos which are paternally rescued by a wild-type copy of Tre1, indicating that while the germ cell migration defects are rescued by a paternal wild-type copy of Tre1, the cell death defect of ectopic germ cells outside the gonad is not rescued by a paternal wild-type copy of Tre1 (since the embryos contain an average of 7.7 germ cells outside the gonad and a higher number of germ cells in total than control embryos). Tre1^sctt/Y males derived from homozygous females are fertile in only 33.7% of crosses. Only 41.7% of Tre1^sctt/Tre1^sctt females derived from homozygous females produce offspring (the remaining females fail to lay eggs). The ovaries are agametic in 57% of cases, rudimentary in 11% of cases and normal in 32% of cases. The gonadal defects correlate with fecundity. Tre1^sctt/+ females derived from homozygous females are as fertile as wild type animals and 97% have normal ovaries.