The indirect flight muscles of pupae carrying Mhc^+memb in a Mhc¹⁰ background assemble circular myofibrils similar to normal indirect flight muscles and show hexagonal packing of thick and thin filaments with sarcomeres containing M- and Z-lines. Adults show progressive disruption of the myofibrils of the indirect flight muscles, such that by 1 week after eclosion thick and thin filaments are scattered throughout the cytoplasm and sarcomeres have abnormal or missing M- and Z-lines.

Flies expressing Mhc^+memb are able to jump only 40% as far as Mhc^+t12.4 expressing flies.

Relaxed tension of tergal depressor of the trochanter (TDT) muscle expressing Mhc^+memb is very low, especially compared to the indirect flight muscles. Net active tension is approximately 30-fold higher than passive tension in Mhc^+memb flies, whereas all myosins tested in the indirect flight muscles exhibit passive tension levels almost equal to net active tension. TDT expressing Mhc^+memb exhibit higher force levels at lower calcium concentrations.

Animals carrying Mhc^+memb in a Mhc¹⁰ background show severe cracking and fraying of myofibrils in the indirect flight muscle. The basic sarcomere pattern is disrupted at 2 days after eclosion and 2 weeks after eclosion, myofibrils are no longer discernible.

Indirect flight muscle (IFM) myofibrils expressing Mhc^+memb in a Mhc¹⁰ background show ultrastructural deterioration, which begins soon after the age at which Drosophila normally begin using the IFMs. These flies cannot beat their wings. These flies can jump, but achieve much shorter differences than wild-type flies.

Flies carrying Mhc^+memb in a Mhc¹⁰ mutant background exhibit normal-looking myofibrils at the pupal stage. In young adults, the myofibrils are disorganised with cracking and fraying throughout. In 1-week old flies, the myofibrils are completely disorganised.

Adults with one copy of P{Mhc^emb} in a wild type background are completely flightless and exhibit a 50% reduction in jumping ability. Two copies of P{Mhc^emb} rescue the embryonic lethal Mhc¹ mutants to adults. Adults do show phenotypic abnormalities: they are completely flightless, have reduced jumping ability, they can walk but are sluggish, often exhibit wings-up phenotype and have an indented thorax. Adults do not mate with each other but do with wild type. The myofibrils of Mhc¹; P{Mhc^emb} indirect flight muscles look normal. Myofibril stability is affected, a few days after eclosion fibrils are cracked and frayed, disruption is more extreme with time. Structure of the jump muscle is normal with only occasional minor deviations in the regularity of thick filament arrangement.