We report an unusual overexpression pattern of the hypomorphic alleles γCop 11a , γCop 14a and γCop 16b of gammaCop gene from Drosophila melanogaster. Each allele contains a distinct short remnant of the P{lacW} transposon located in 5'UTR. Repeated crosses between γCop 14a /γCop 14a females and γCop 11a /γCop 11a or γCop 16b /γCop 16b males proved to be sterile, but the reciprocal ones are fertile.The most severe allele is γCop 14a since a γCop 14a /γCop 14a line cannot be obtained. Remarkably, qRT-PCR performed on mutant eggs, testes and embryos reveals that γCop 11a , γCop 14a and γCop 16b are overexpressed, which is counterintuitive for hypomorphic alleles. Moreover, the expression scale overlaps the hierarchy of the allelic phenotype severity.We found that the folding ΔG values of the mutant 5'UTRs are very low as compared to the folding ΔG value of the wild-type 5'UTR. This thermodynamic context may account for the uncommon expression pattern of the hypomorphic alleles described herein.