米象、玉米象及其杂交后代染色体的观察研究

本研究观察表明,米象sitophilus oryzac 与玉米象Sitephilus zcamsis 的染色体数目都是22条(2n=22).它们的第1—10对同源染色体及第①条非同源染色体的相对长度和着丝点类型基本相同.第②条非同源染色体,米象为中部着丝点类型,玉米象为端部着丝点类型.米象与玉米象杂交可育型后代的染色体出现杂交Ⅰ杂种及杂交Ⅱ杂种两类染色体.杂交Ⅰ杂种染色体倾向于米象,杂交Ⅱ杂种染色体的第10对同源染色体为端部着丝点类型,与米象及玉米象的都不同.

OBSERVATION ON THE KARYOTYPES OF SITOPHILUS ORYZAE AND SITOPHILUS ZEAMAIS AND THEIR HYBRID OFFSPRINGS

Sitophilus oryzae and 5. zeamais are the two snout beetles showing close resemblance and their identification'has caused controversy in the past. We carried out cross experiments for four years and found that the cross-breeding was difficult and the progenies were mostly sterile but about 3% of them were fertile and could produce fertile offsprings. A microscopical examination of the karyotypes revealed that both species contained 22 chromosomes (2n = 22) and-the relative length and centromere pattern of the homologous chromosomes from the first to the tenth pairs and the first pair of nonhornalogous chromosome ate similar. However, the second nonhemologous of; 5. oryzae is metacentric while that of S. zeamais telocentric. There are two karyotypes in the fertile crossbreeds: one is similar to that of S. oryzae and the other-is different from the both species in having the tenth pair of homologous chromosomes being telocentrie.