Kallman K D, Bao I Y
J Exp Zool. 1987 Jul;243(1):93-102. doi: 10.1002/jez.1402430112.
The sex-determining mechanism of swordtails (Xiphophorus, Poeciliidae, Pisces) is poorly understood, because many laboratory strains of these species are characterized by biased sex ratios in either the male or female direction. Because of these ratios sex determination is said to be controlled by numerous male and female factors scattered over many chromosomes. However, direct experimental evidence for the polygenic theory is absent. Three strains of X. alvarezi were derived from natural populations in Guatemala, two of which (Dolores, Candelaria) always exhibit a ratio of 1:1, whereas the third one (San Ramón) shows a preponderance of males. Males of X. alvarezi, like those of other species of swordtails, develop a caudal appendage or sword at maturity. Chromatophores with carotenoid pigment (orange) are present in the sword of Dolores males and pigment cells containing sepiapterin (green) are present in the swords of males and the other two stocks. F1 and backcross hybrids were produced between the Dolores and Candelaria stocks. The sex ratios of all hybrid pedigrees was always in statistical agreement with unity. The pattern of inheritance of the two pigmentary traits demonstrated sex-linkage with female heterogamety (WY female female-YY male male).
剑尾鱼（Xiphophorus，花鳉科，硬骨鱼纲）的性别决定机制尚不清楚，因为这些物种的许多实验室品系都具有偏向雄性或雌性的性别比例特征。由于这些比例，据说性别决定受分布在许多染色体上的众多雄性和雌性因素控制。然而，多基因理论缺乏直接的实验证据。三株阿氏剑尾鱼（X. alvarezi）源自危地马拉的自然种群，其中两株（多洛雷斯、坎德拉里亚）的性别比例始终为1:1，而第三株（圣拉蒙）雄性占优势。阿氏剑尾鱼的雄性与其他剑尾鱼物种的雄性一样，在成熟时会发育出尾鳍附属物或剑尾。多洛雷斯雄性剑尾中存在含有类胡萝卜素色素（橙色）的色素细胞，而雄性剑尾以及另外两个品系的剑尾中存在含有蝶啶（绿色）的色素细胞。在多洛雷斯和坎德拉里亚品系之间产生了F1和回交杂种。所有杂交谱系的性别比例在统计学上均与1一致。两种色素性状的遗传模式表明其与雌性异配（WY雌性 - YY雄性）存在性连锁。
