- Drosophila is characterised by sexual dimorphism. Males can also easily be distinguished from females which have variations in size and colour. - The female's length, however, is approx. Moreover, 2.5 mm, male is slightly smaller than female with darker dorsal sites of the male body due to a separate black patch at the abdomen.- In our understanding of heredity, the sex chromosomes of the Drosophila melanogaster fruit fly have played a especially important role. - Therefore, it can come as a surprise that a relatively unusual method for deciding sex is used by fruit flies. In Drosophila, sex is mainly determined by the X: A ratio, or the ratio of the number of X chromosomes to the number of autosomal sets (Cline & Meyer, 1996). - The balance between encoded female-determining factors on the X chromosome and encoded male-determining factors on the autosomes decides the transcription sex-specific pattern will be initiated. - Thus, females are XX, XXY, and XXYY flies, while males are XY and XO flies. With more than two copies of an X chromosome, flies are unable to survive because of the mechanism they use for dose compensation. Dosage compensation refers to the mechanisms by which animals equalise the amount of gene products in males and females derived from X-linked genes. - Unlike in mammals, all of the Drosophila X chromosomes remain involved, and by doubling the expression of the X chromosome in males, flies change the levels of X-linked gene products. - An additional copy of the X chromosome, containing approximately one-third of the fly genes, causes an aneuploid syndrome that substantially disrupts cell balance.