Duplication or insertion of a wild-type copy of Ser onto the SerBd-3 chromosome, thus the chromosome carries both one normal Ser[+] copy plus the SerBd-3 antimorphic allele.
male fertile
wing | anterior
wing vein
Heterozygotes exhibit phenotypically normal wings. Heterozygotes with Df(3R)Dl-BX6 exhibit loss of anterior wing margin and thickening of wing veins.