Formation of unreduced eggs has been reported in several interspecific hybrids of teleosts.These results suggested that a genomic conflict due to a hybrid event may trigger an atypical mode of reproduction,such as formation of unreduced gametes.The diploid gynogenetic progenys of allotetraploid hybrids of red crucian carp(Carassius auratus var.red)×common carp(Cyprinus carpio L.)(abbreviated as G)produced diploid eggs,which have been identified by chromosomal counting of germ cells,fertilization observation of gametes and ploidy detection of progeny.In this paper,DNA contents and cytological studies on oogenesis of G was detected by Flow Cytometry,tissue sections and chromosomal observations,with dipoid red crucian carp as controls.The results showed that the DNA contents of oocytes in G were showed with two main peaks.The peak one with the lower value was consistent and the other peak value was double with that of oocytes in RCC,which were deduced as different type of primary oocytes by tissue sections observations and chromosomal observations.The oocytes with lower peak values showed the mainly smaller volume of primary oocytes,in which there were some cavitation-like abnormal oocytes,exhibiting partical pairing at the pachytene stage,they were deduced as the primary oocytes without chromosomal doubling.Such other oocytes with higher peak values showed a few larger volume of primary oocytes in stage Ⅱ,which could perform normal development with normal chromosomal pairing in meiosis Ⅰ,and were deduced as the primary oocytes with chromosomal doubling.The results enriched the research data of mechanism of unreduced gametes,being of great significance in fish genetic breeding.