We must distinguish clearly between sex-linked and sex limited characteristics. As already pointed out, geneticists have placed so much emphasis on the gene characteristics which are located on the Y-chromosome that almost everyone now believes that to obtain super guppies all one must do is to obtain a super male; that the female plays but little part in passing on the more cherished features. This is only partly true. The characteristics produced by genes on the Y- chromosome are sex-linked.
 The beautiful plumage of a male chicken is quite different from the hen's. Is it sex-linked? No. If the young chicks of both sexes are caponized, the resulting mature birds look very much alike. The capon looks like the hen, the caponized female chick looks much like the capon. These particularly masculine and feminine characters are determined by glandular secretions-hormones-and are sex-limited. What sex-limited characteristics do we find in guppies?
 There have been few studies which help us much . Female guppies which have been masculinized by hormone treatments cannot exhibit any features which their female genes cannot develop. All they can show are characteristics which their female hormones have repressed. A number of male-like features show up, and all of these are evidence that such are not on the Y chromosome. The beautiful colors now being bred on female guppies' tails are not functions of the Y chromosome. Indeed the plainness of the female is partly due to hormones which restrict some of the beauty from appearing. Male hormones fed to partly grown females inhibit their growth.
 The cessation of growth in males at the time they reach sexual maturity is a sex-limited character. When treated with female hormone, they grow much larger.