GENETIC CONTROL MECHANISMS OF SEX DETERMINATION IN ORYZIAS FISHES

(1)通过体色的性别连锁遗传和人工性别逆转鱼的后代测试，证明了米达卡鱼具有XX雌性/XY雄性的性别决定系统。这仍然是一个悬而未决的问题，然而，X或Y在这种鱼的性别决定过程中有决定性的作用。本实验培育了三倍体鱼，并研究了性染色体组成与鱼的性别之间的关系。得到的XXX鱼均为雌性，而XXY鱼为雄性，表明Y上的基因决定了鱼的性别分化为雄性（显性-Y系统）。(2)除奥米亚鱼（Oryzias latipes）外，奥米亚鱼的性别决定系统至今尚未明确。我们培育了曲维诺鱼雌化二倍体，并通过对幼鱼性腺的组织学观察来鉴定其性别。本研究共获得13条雌性纯合子，均为雌性，结果表明曲维鱼也具有XX*-XY*性别决定系统。(3)测定了弯叶蛇与弯叶蛇近交系（HdrR系和HNI系，前者来自南方种群，后者来自北方种群）种间杂种的性别。所有HdrR菌株与弯叶稻的种间杂种（X^<HdrR> Y^< 0）。曲形鱼（Curvlnotus >）是雌性鱼发育的卵巢。另一方面，HNI菌株与O.curvinotus杂交产生两性后代，即X^<HN1> Y^< 0。曲维诺图斯为雄性。这些结果可以解释为，Y染色体上的性别决定基因（SDY）需要一些额外的遗传因素来决定个体的性别，而曲线鱼的SDY与HdrR因素不相容，而与HNI因素相容。我们对HNI和HdrR进行了遗传分析，以确定影响因素。HNI和HdrR之间的F1鱼与弯尾鱼配种，种间杂交种均为雌性。然后，将F1鱼与HNI鱼杂交后的鱼与曲线鱼进行交配。所有的后代都是雌性。这些结果表明，影响米子鱼性别决定的遗传因素并不少。进一步的基因分析正在进行中。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