The reporter learned from Southwest University that Professor Dai Fangyin's team has obtained the complete genome sequence of the W chromosome of the silkworm for the first time through research, revealing a new mechanism for the origin and evolution of the W chromosome in Lepidoptera insects. This research achievement has important theoretical significance in the field of genomics and evolutionary biology, and brings new prospects for molecular breeding of silkworms. It has recently been published in the sub issue of Science, Scientific Progress. It is reported that the composition of sex chromosomes in the animal kingdom presents rich diversity. In mammals, the sex chromosome composition of males is usually XY, while females are XX, and gender is determined by key genes on the Y chromosome. Birds have a ZW chromosome system, with males being ZZ and females being ZW. In insects, the sex chromosome composition is mainly composed of the XX/XY system. But Lepidoptera insects are different from most other insects, and their sex chromosomes are mainly composed of the ZZ/ZW system. Therefore, the origin and evolution of the W chromosome in Lepidoptera insects have received long-term attention from evolutionary biologists. In the past 20 years, the research on the molecular mechanism of sex determination in silkworms has been a hot topic, but the mechanism of sex determination in silkworms has not been clearly analyzed, which is related to the lack of information on the W chromosome sequence of silkworms. The first author of the paper and associate professor of the National Key Laboratory for Efficient Breeding and Utilization of Resource Insects at Southwest University, Han Minjin, introduced that the team applied second-generation short read long, third-generation long read long, and Hi-C sequencing technology to assemble the chromosome level genome of female silkworm individuals, and developed a tool for identifying W chromosomes rich in repetitive sequences, obtaining a W chromosome sequence of about 10.1Mb in length. Research has found that the W chromosome of silkworms contains 137 copies of the female sex determining factor Fem and 76 protein coding genes. This information is of great value for deciphering the sex determining mechanism of silkworms and molecular breeding based on the W chromosome. The study also compared the genomes of 21 Lepidoptera insects and 3 Trichoptera insects, revealing that the W chromosome of Lepidoptera insects is independently generated through multiple mechanisms, and proposed a new mechanism for the formation of the W chromosome in Lepidoptera - single Z chromosome transformation, providing new insights into the origin and evolution of the W chromosome in Lepidoptera insects. (Lai Xin She)
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