Homozygous and tw^unspecified/Df(1)Exel6223 adults show significantly decreased climbing ability compared to control flies. The mutant flies also have reduced flight ability compared to controls. The general locomotive activities of hemizygous flies are not significantly different from wild type.

Mutant larvae show abnormalities in the body wall muscles, with defects in muscle patterning often being seen, and muscles occasionally being missing.

Mutant adults have ultrastructural defects in the thoracic and leg muscles. Sarcomeric disarray is often seen, Z-lines are irregular and often streaming, actin and myosin filaments are disorganised and accumulations of glycogen granules are seen. Enlarged mitochondria and swollen sarcoplasmic reticulum are seen between the muscle fibres. The basement membrane is duplicated and multilayered. Muscle defects are seen in both 15- and 35-day old adults, but are more frequent in the older flies.

The wing disc area occupied by myoblasts in mutant thid larval instar discs is less than that in control disc. However, the number of myoblast per unit area of tissue is higher in the mutant discs than in the control discs, and as a result, the total number of myoblasts per disc is not significantly different in mutant and wild-type discs. The number of apoptotic myoblasts is 2.4 fold higher in mutant wing discs than in controls, while the number of dividing myoblasts per disc is not different in mutant and wild-type discs.

Crosses of heterozygous females to hemizygous males result in significantly lower mutant adults than expected, indicating a reduction in viability.