21. Assume that mutations in the transformer (tra) and the male- specific lethal (MSL) genes eliminate the Sxl binding sites in the RNA transcribed from these genes. How would these mutations influence the sexual development of the fly embryo? Solution SXL gene is the master regulator of sex determination in drosophila so mutation in the Sxl binding sites will leads to mutant female that prevented from making eggs by protein coding lesion in SXL. Such mutations have no effect on sex determination in XY males. Homozygosity of the intersex (ix) gene causes XX flies to develop an intersex phenotype having portions of male and female tissue in the same organ..