Heterozygotes have an indented thorax, upheld wings, and are flightless. Hemizygotes are semi-lethal. They are very inactive, with weak mesothoracic legs that are generally folded beneath the thorax, and die prematurely after eclosion.

Heterozygotes display indented thorax and erect wings; flightless; hemizygotes semi-lethal, very inactive, have weak mesothoracic legs which are generally folded beneath the thorax; die prematurely after eclosion. Judged to be antimorphic since not rescued by addition of Dp(2;3)osp³. Mhc¹⁶ interaction in double heterozygotes with other flightless mutants observed by Homyk and Emerson (1988). Heterozygous viability severely reduced in combination with hemizygous wupA^hdp-2, up^int-3, up¹⁰¹; or up^x; rare escapers have gnarled legs, walk poorly and die within two days of eclosion.