Mixed up confusion
Males and females of most species differ in several characteristics. But strangely, this is most obviously so with regard to traits that have no direct relation whatsoever to their reproductive functioning as males or females. Size, colour and pattern in birds and butterflies for instance and song in cicadas and frogs, and so on. The implication is that males are often better off possessing one version of a trait than the females, who do better with another.
In fact, some traits may be advantageous to one sex but positively disadvantageous to the other. This intriguing proposition has now been put to the test by W R Rice of the University of California, USA.
Rice worked with the fruit fly Drosophila melanogaster and carried out the test by developing a synthetic y-chromosome which was not only contained extra genes normally belonging to other chromosomes, but also, just like the real y-chromosome, was passed only from father to son. This synthetic chromosome was maintained within males for 41 generations. Presumably, while being thus maintained, it must have accumulated mutations that helped it and the mates that carried it. However, would these mutations be detrimental to females? By using genetic tricks. Rice was able to transfer the extra genes on the synthetic y-chromosome to females. The results were clear and striking: females that received this chromosome after 29 generations of passage through the male line did far more poorly than females who received the starting version of the same set of genes. Normal y-chromosome may also have evolved similarly: by being restricted to males, it has become so harmful to females that it presence is incompatible with even development as a female, let alone success.