80-85% of up^int-1 flies hold wings ventrolaterally, 10% hold them vertically and the remainder maintain normal wing position. In many flies mesonotum indented to variable degree and at various positions; 85% in flies raised at 29^oC and 45% when raised at 18^oC. More extreme expression in y flies; partially dominant in y genotypes. Fate mapping indicates focus in presumptive thoracic musculature. Indirect flight muscle structure badly deranged, Z-bands disappear as muscles degenerate; also lose a 54k protein. up^int-1/up^int-1 adults flightless and unable to jump; up^int-1/+ adults normal.

In many up^int-1 flies, the dorsal thorax is indented. The position and extent of the indentation is variable with indentations observed at a higher proportion (85%) in flies raised at 29^oC, than in flies raised at 18^oC (45%).

100% of up^int-1 flies are flightless and jumpless, regardless of temperature. 80-85% of up^int-1 flies hold their wings ventrolaterally, 10% hold them vertically and the remainder have them in a normal position.