二倍体雌核发育鱼产生二倍体卵子的证据

Evidence of the Unreduced Diploid Eggs Generated from the Diploid Gynogenetic Progeny of Allotetraploid Hybrids

二倍体雌核发育第 1代 (G1)产生的二倍体卵子经紫外线灭活的散鳞镜鲤精子诱导 ,无需染色体加倍处理 ,发育成二倍体雌核发育第 2代 (G2 ) ;G1 产生的二倍体卵子与雄性异源四倍体鲫鲤 (AT)产生的二倍体精子结合 ,形成新型两性可育的异源四倍体鲫鲤 (G1 ×AT)。对G2 和新四倍体 (G1 ×AT)的体细胞染色体数目、生殖细胞染色体行为及性腺结构、外形、生长速度等生物学特征进行了研究。结果表明 :G2 体细胞染色体数目为 2n =1 0 0。在 6～ 1 2月龄G2 中 ,没有发现性成熟的个体 ,组织学切片结果表明 ,G2 性腺处于卵原细胞增殖阶段 ,与 1龄G1 的性腺发育相似 ,性腺发育迟缓。对 6～ 8个月龄G2 性腺染色体制片进行观察 ,结果表明 ,G2 生殖细胞的染色体没有二价体的形成 ,只有有丝分裂的迹象 ,其有丝分裂中期不但有 2n =1 0 0的染色体分裂相 ,还有 4n =2 0 0的染色体分裂相 ,甚至有接近 8n(380 )的分裂相 ,说明 1龄G2 的性腺中存在 2n、4n等多种类型的生殖细胞 ,其中 4n的生殖细胞经正常的减数分裂后可产生二倍体卵子。核内复制 (pre meioticendoreduplication)学说可以较好地解释这种不减半配子产生的现象。新四倍体 (G1 ×AT)体细胞染色体数目为 4n =2 0 0 ,雌雄新四倍体 (G1 ×AT)具有正常的性腺发育 。

Following activation by UV-irradiated sperms from scatter scale common carp and without the treatment for doubling the chromosome number,the eggs generated by the diploid gynogenetic progeny (G_1) with 100 chromosomes,developed into diploid gynogenetic progeny (G_2) with 100 chromosomes.Both the males and females of the tetraploids with 200 chromosomes were obtained from the offsprings (G_1×AT) produced by mating the eggs of G_1 with the diploid sperms from the allotetraploid hybrids.The results provided the evidence that diploid G_1 is able to produce diploid eggs.In the oogonia of diploid six-month old G_2,only the chromosomes in the metaphase of mitosis were observed in all slides,no bivalent chromosome being found,suggesting that the oogonia in six-month old G_2 were not mature enough for meiosis Ⅰ.The presence of the chromosome spreads with 100,200 and 380 chromosomes observed in the metaphase indicated that the diploid G_2 had the potential ability to generate diploid eggs with the probable mechanism of pre-meiotic endoreduplication.In contrast,the spermatocytes of G_1×AT allotetraploids had the normal chromosomal behavior with only 100 bivalents found in meiosis Ⅰ.The one-year old G_2 possessed the slowly developmental ovaries which stayed at the oogonium stage for a long time,in which no primary and mature oocyte was found,whereas both the females and males of one-year old G_1×AT allotetraploids had normal ovaries and testes which reached maturity and produced diploid eggs and diploid sperms,respectively.The formation of the diploid eggs generated from the diploid gynogenetic progeny makes it available to establish a diploid hybrid clonal line,and will become an important source of production of diploid eggs.In addition,the bisexual fertile G_1×AT allotetraploids enriched the types of the tetraploids.