中国银额果蝇自然群体B染色体的分布

经对我国银额果蝇自然群体Ｂ染色体（Ｂｓ）的分布进行多年广泛地调查，共作过２４个群体，５７２个单雌系，６７３８只个体的观察。从细胞和群体水平研究Ｂｓ的地理分布。结果发现，中国（除台湾省外）银额果蝇自然群体中普遍存在Ｂｓ。结合前人报道得出。Ｂｓ的地理分布出现了由东向西和由南向北的规律性的依次升高趋势。这种跨越不同地理环境的区域性梯度变异与其宿主向大陆内地扩散的推论相符。Ｂｓ频率最高（８７．７％）的是海

GEOGRAPHICAL DISTRIBUTION OF Bs IN NATURAL POPULATIONS OF Drosophila albomicans FROM CHINA

In the past years,we have extensively investigated the geographic distribution of B chromosomes (Bs) in natural populations of Drosophila albomicans in China.The karyotypes of 6?738 individuals from 572 isofemale lines in 24 populations were scored.The results revealed that Bs were widely distributed in all populations except Taiwan population.The number of Bs varied from 0 to 14 in different individuals.The frequency of occurrence was the highest in Hainan population,in which 87 7 percent of the individuals contained B chromosomes.Interestingly,we found the occurrence of Bs in D.albomicans displayed a cline pattern:the frequency increased from east to west,from south to north.Furthermore,correlation was found between Bs frequency and ecological condition of habitat.In terms of this correlation,we categorized these 24 populations into 5 ecological types:1) coastal hilly land populations,2)plateau populations,3) island populations,4) mountain populations,and 5) canyon populations.