title: A chromosomal investigation of four species of Chinese Panorpidae (Insecta, Mecoptera).
abstract: The male adults of four species of the Chinese Panorpidae in Mecoptera were cytogenetically studied using conventional squashing procedures. The results show that their sex-chromosome system belongs to the XO type, with n = 19 + X(O) in Panorpa emarginata Cheng, 1949 and Panorpa dubia Chou & Wang, 1981, n = 23 + X(O) in Panorpa sp., and n = 20 + X(O) in Neopanorpa lui Chou & Ran, 1981. X chromosomes of these species usually appear dot-shaped in late prophase I and are easily differentiated from autosomal bivalents. Meiosis in these Panorpidae lacks typical diplotene and diakinesis. In late prophase I, pairs of homologous chromosomes remain parallel in a line and show no evidence of crossing-over. Some of them even appear as a single unit because of extremely intimate association, all with a tendency of increasing condensation. The evolutionary significance of their chromosomal differences and the achiasmatic meiosis of Panorpidae are briefly discussed.
authors.affiliation: College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Yankai
authors.initials: Y
authors.lastname: Li
authors.forename: Baozhen
authors.initials: B
authors.lastname: Hua
keywords: Mecoptera; Panorpidae; XO sex-chromosome system; achiasmatic male meiosis; chromosome