GENETIC CONTROL MECHANISMS OF SEX DETERMINATION IN ORYZIAS FISHES

(1)青竹具有XX雌性/XY雄性的性别决定系统，通过体色的性别连锁遗传以及人工性别反转鱼类的后代测试，证明了青竹具有XX雌性/XY雄性性别决定系统。然而，这仍然是一个悬而未决的问题，无论是X还是Y在这种鱼的性别决定过程中都起着决定性的作用。本实验获得了三倍体鱼类，并对其性别与染色体组成的关系进行了研究。所获得的XXX鱼均为雌性，而XXY均为雄性，这表明Y上的基因(S)决定了鱼类向雄性的性别分化(显性-Y系统)。(2)除宽叶水稻外，其他稻属鱼类的性别决定系统尚不清楚。通过对幼鱼性腺的组织学观察，获得了雌核发育二倍体的曲纹东方鱼，并对其进行了性别鉴定。我们获得了13条雌核发育纯合子鱼，均为雌性，I…(3)对曲纹野生稻和宽叶野生稻(HdrR和HNI品系，前者来自南方群体，后者来自北方群体)的种间杂种进行了性别鉴定。HdrR品系与Curvinotus(X^&lt；HdrR&gt；Y^&lt；O.Curvlnotus&gt；)的种间杂交均为雌性鱼类发育卵巢。另一方面，HNI品系与柯氏田鼠的杂交产生了两性后代，即X^&lt；HN1&gt；Y^&lt；O.curvinotus&gt；这些结果可以解释Y染色体上的性别决定基因(SDY)需要一些额外的遗传因素(S)来决定个体的性别，而曲纹东方田鼠的SDY与HdrR因素是不相容的，而与HNI的因素是相容的。用HNI与HdrR杂交的F1鱼与柯氏野生稻交配，得到的种间杂交种均为雌性。然后，将F1鱼与HNI杂交得到的鱼与Curvinotus交配。所有的后代也都是雌性。这些结果表明，不少遗传因素可能参与了稻属鱼类的性别决定。进一步的基因分析正在进行中。较少

(1) The medaka, Oryzias latipes has been demonstrated to have an XX female/XY male sex-determination system by the sex-linked inheritance of body color as well as by the progeny test of the artificially sex-reversed fish. It is still an open question, however, either the X or the Y has a definitive role in the sex determination process of this fish. In the present experiment, triploid fish were produced, and the relationship between the sex choromosome composition and the sex of the fish were examined. All XXX fish obtained were female, whereas XXY were male, suggesting that the gene (s) on the Y determines the sex differentiation of the fish into male (dominant-Y system).(2) The sex-determination system of Oryzias fishes except Oryzias latipes has not been clarified so far. We produced gynogenetic diploid fish of O.curvinotus and examined their sex from the histological observations on the gonads of juvenile fish. We obtained 13 gynogenetic homozygous fish, all of which were female, i … More ndication that O.curvinotus also has an XX*-XY* sex-determination system.(3) We examined the sex of the interspecific hybrids between inbred strains of O.curvinotus and O.latipes (HdrR and HNI strains, the former originated from the Southern Population and the latter from the Northern Population). All the interspecific hybrids between HdrR strain and O.curvinotus (X^<HdrR> Y^<O.curvlnotus>) were female fish develop ovaries. On the other hand, the cross between HNI strain and O.curvinotus yields offsprings of both sex, that is X^<HN1> Y^<O.curvinotus> were male. These results can be interpreted that the sex determining gene on Y chromosome (SDY) need some additional genetic factor (s) to determine the sex of the individual, and the SDY of O.curvinotus is incompatible to the factors of HdrR whereas compatible to those of HNI.We conducted genetic analysis between HNI and HdrR to identify the factors. F1 fish between HNI and HdrR were mated to O.curvinotus, and all the interspecific hybrid from these cross were female. Then, the fish from the cross between F1 fish and HNI were mated with O.curvinotus. All the offsprings were also female. These results indicates that not a few genetic factors can be involved in the sex determination of Oryzias fishes. Further genetic analysis is in progress. Less