| Chromosome is the carrier of inheritance material, whose structures and functions are the most important content of cytogenetics. With the development of molecular biology techniques. molecLIlar biological techniques are now being gradually applied in the studies on chromosomes, especially. Fluorescence in situ hybridization (FISH) has become a bridge between c~'togenetics and molecular genetics~ more and more researches have been carried out to sho~~ light on the structures and functions of chromosomes at the molecular level. The cytogenetics of Fri-silkworms was hindered by the specialities of their chromosomes, such as the little morphological difference among chromosomes, the small rod, even particle morphology during metaphase, non-fixed centromere, no arm-ratio and difficultly banding, et al. Therefore. it is urgent to accelerate the development of Eei-silkworms by using molecular cytogenetical techniques.This dissertation, on the basis of other researches, is to enrich the cytogenetics of [ri-silkworms, on the other hand is to apply new techniques of molecular cytogenetics in the studies on chromosomes of Fri-silkworms. The results are summed up as following:(1) Studies on the chromosome of wild silkworm, Bombyx mandarinaThe chromosomal morphological characters and behaviors in the oocytes of mulberry wild silkworm, Bombvx mandarina were compared with those of spermatocytes during meiotic prophase I. The findings proved that chromosomes in oocytes are linked completely, whereas, crossing-over happens on chromosomes in spermatocytes from the point of cytogenetics. At the same time, "Y"-bifurcated ZW bivalents were observed at pachytene stage of oocytes, which suggests that the type of sex chromosome is ZZ-ZW and a kind of equalization has happened during synaptic stage. Moreover, the chromosome number of 13.rnundarina in three regions of China, (ie. Chongqing, Shanxi, Hubei) is all 2n56. The light-stained G-band bivalents were found at pachytene stage that were similar to those of Bomhyx mon. whose karyotypes were analyzed, which supported the view that there is a high homology of chromosomes between B. mon and B. mandarina.VI(2)Studies on the cytogcnetics of Phiosamia riciniMitotic course of Philosanzia ricini was first to be observed and the chromosomal features of different rnitotic stages were described in detail. The chromosomal differences during meiotic prophase I between spermatocytes and oocytes were illustrated, which proved that the chromosome of oocytes are linked completely, whereas, crossing-over and recotnbination happen. on the chromosome of spermatocytes on the basis of cytogenetical points. At the same time, the morphological characters and behaviors of sex chromosome at diplotene stage were observed in detail. Moreover, through the comparison of karyotypes of different phases, it is necessary to refer to karyotypes of different stages one another when the karyotypes of En-silkworm are analyzed.(3) RFLP analyses for genomes of B. mandarina and P ricini and B.moriThe homologous sequences of lihroin heavy chain gene (Fih-Jh. sencin I gene (Se,'!) and chymotrvpsin inhihitoi' 13 gene (Cl-IS) of B. mo/i were found to he in the genonme of' I~. munclcirinc, and P ricini h~ Southern blotting. Moreover. RFLPs analyses showed that there are the same enzymic cleavage sites in the genome of B.mori and 13.nzandurina. It also suggested that the increase in efficiency of fibroin biosynthesis of I3.mori, which has been acquired through selection during domesticated, is caused by an increase of ploid\ in the silk gland cell nucleus or by mutational changes in genes related too transcriptional or post-transcriptional machinery in B.mori trains but not by an alternation in the structure of the fihroin gene itself.(4)FISH Studies on the chromosomes of B.mori and B.mandarina[he locations ol' ,S'e,I and ('1-13 on the chromosome of Bmori were certified h~ FISI-I and the results showed that SeiJ is on near terminal of the 11 linkage group. which is... |
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