基于45S rDNA和雷蒙德氏棉gDNA为探针的草棉FISH核型研究

 草棉基于荧光原位杂交（FISH）的核型公式为2n = 2x = 26 = 16m + 10sm (6 sat)，短臂和长臂的相对长度分别为1.43～4.14和3.34～5.18，染色体长度比(最长与最短染色体的比值)是1.63。染色体组有6个随体，都定位在最后3条染色体的短臂上，其中位于第12和第13号染色体的随体在DAPI和罗丹明镜像中明显可见，但位于第11号染色体的随体在DAPI镜像中观察不到。检测到6个(3对)NOR信号，与随体同位，1对位于染色体端粒，2对紧接着丝粒。雷蒙德氏棉基因组DNA（gDNA）作探针时，在体细胞染色体上检测到GISH-NOR，其数量、位置和大小与45S探针的NOR相同，说明FISH核型比以前常规核型（非FISH核型）更精确。结合本试验室其它FISH资料，推断A基因组棉种在作为供体形成异源四倍体棉种以来，一些串连重复序列如rDNA可能发生了很大变化，包括扩增、易位或缺失等。对于D基因组特有的GISH-NOR的一个可能解释，就是D基因组棉种的rDNA拷贝数远远多于A基因组棉种。NOR或者GISH-NOR位点等方面的进一步研究，有助于探讨rDNA基因进化和功能，并作为一种标记应用于棉属构建染色体序号定位的物理图谱。

FISH-based Karyotype of Gossypium herbaceum Generated with 45S Rdna and Gdna of Gossypium raimondii as Probes

The formula for FISH-based karyotype of Gossypium herbaceum was as 2n = 2x = 26 = 16 m + 10 sm (6 sat), with the range in relative length of short and long arms from 1.43 to 4.14, 3.34 to 5.18, respectively. The ratio between the largest chromosomes and the smallest one was 1.63. Six satellite loci were mapped on short arms of the last three chromosomes. The satellites on chromosomes 12 and 13 were clearly visable in both DAPI and rhodamine/DAPI images, however the satellite on chromosome 11 was not detected in DAPI images.Six, in three pairs, of NORs were observed adjacent to the satellite sites, with one pair on telomere and two pairs near centromeres. When gDNA from G. raimondii was used as probe, GISH-NORs were scored in mitotic chromosomes of G. herbaceum with the same numbers, locations and sizes as 45S rDNA NORs. It could be therefore concluded that FISH-based karyotype analyses were more detailed than previous karyotype (non-FISH). Based on this study in conjunction with our other FISH results, there might be great amplifications or pericentric inversions of rDNA in modern A genome species after its contribution to allotetraploid originations, or deamplifications/deletions of tandem repeats like rDNA in extant allotetraploids following their polyploidization. An explanation to D genome specific GISH-NORs is that rDNA contents in D genome species may be much more than those in A genome species. The NORs or GISH-NORs herein may facilitate future locus-specific studies on rRNA gene evolution and function, and also may be useful in developing physical map specific to chromosome order in Gossypium.