Crossing scheme to obtain all-male broods from estrogen sex-reversed fish. Sexually undifferentiated fry including both, XX- and XY-genotypes, were treated with estrogen resulting in only phenotypical females. These females – genetic females and sex-reversed genotypic males – were then crossed to untreated genotypic males. Crossing of XX-females to untreated males (left site) reflect the normal reproduction with a sex ratio of 1:1, with the corresponding female XX and male XY genotypes in the offspring. Crossing of sex-reversed XY-females to untreated XY-males led to a sex ratio of 1:3 with the genotypes XX (phenotype female), XY (phenotype male), YY (super male, phenotype male). These two types of phenotypically undistinguishable males were back-crossed to normal XX-females resulting again in either a 1:1 sex ratio (for XY-males) or in all-male broods (for the YY-male). Pink and blue outer circles denote phenotypic females and males, respectively.