The aim of the present investigation was to study the developmental genetic effects of temperature, heat-shock and genetic combinations on rosy (ry) locus in Drosophila. rosy proved to be one of the most important genes in Drosophila because rosy eye-coloured flies, from the homozygous viable rosy⁵⁰⁶/rosy⁵⁰⁶, were the background M cytotype strain used in genetic transformation via P-element mediated method. So, the research was focused on determining the suitable developmental time of gene expression. The approach of temperature sensitivity as well as the gene-dose dependent interaction technique were applied in this respect.                 As it revealed from the results, the lethal phase analysis for [ry506/Df(3)ry81], [oho-31/+;ry⁵⁰⁶/+], [oho-31/+;Df(3)ry81/+], [] and  [;Df(3)ry81/+] genetic combinations were shown to take place during larval stage of Drosophila. Temperature sensitivity studies also showed that the most effective and proper time of gene expression starts as early in the development as in fertilized eggs and lasts up to the end of the third larval instar. Heat-shock experiments and data about the formation of white puparium indicated that the products of the rosy gene expression are mostly needed during the first 40®100 hrs of the development of the insect. Results about the (oho-3,ry) and (arm,ry) genetic interactions suggested that the products of these three genes have to be supplied in sufficient concentrations to maintain the normal phenotype of the animal. Overall, the rosy locus, as a factor on the third chromosome, seemed to have an effect on the level of both arm and oho-31 gene expression in Drosophila. These findings have relevance to possible future applications of these methods in very important genetic loci in insects and mammalian.