5.5kb Tirant insertion within 5' flanking sequences.
Laid eggs fail to hatch, embryos complete embryogenesis but have deletions of anterior and posterior structures. Wild type sperm or sperm carrying duplications of the 21B region cannot rescue embryonic lethality. Female sterile when heterozygous with other Gs1 alleles.
No P-element insert near or in the Gs1 locus.