Chromosome characterization of Bombyx mori and Bombyx mandayina using pachytene chromosomes

Abstract

The chromosome karyotyping of insects included Lepidoptera is very difficult because of the large number of chromosomes, small size, and lack of major constriction structure. This has been a great hindrance to the karyological analysis. In this study, using banding analysis on the pachytene chromosomes, all chromosomes were characterized, and idiograms of Bombyx mori and R mandarina were established. From the testes during meiosis, 81 and 56 cells were examined for the analysis of B. mori and R mandarina, respectively. The best preparation of pachytene chromosomes was obtained on the 3(rd) day of the 3(rd) larva and 2(nd) or 3(rd) day of the 4(th) larva of the B. mori male, and it revealed that there was a characteristic nucleolus structure in the 2(nd) chromosomes, which was supposed to be the Z sex chromosome. The length of the pachytene chromosome was variable during the developmental stage of the cell, so the physical length of each chromosome was relatively converted in comparison to the total chromosome length. Based on the banding pattern and the relative length of the chromosome, the idiograms of the domestic silk worm and the wild one were established. The absence of any differences between C- and G-banding patterns proved that the holocentric chromosome of these organisms and the similarity of banding patterns in chromosome 2, 25, 26, 27, and 28 in R mori and chromosome 2, 24, 25, 26, and 27 in B. mandarina suggest their phylogenetic similarity in evolution.