Further construction of proximal duplication stocks
--Zheng, Y-Z; Carlson, WR

B-A translocations can be used to construct unusual stocks, referred to as proximal duplication stocks. For example, 9-BSb 9-BSb 9-BLa 9-BLa is a proximal duplication stock. It was constructed by combining the 9-BSb from TB-9Sb with the 9-BLa from TB-9La. The B-9Sb and B-9La were discarded (Carlson and Curtis, Can. J. Genet. Cytol. 28:1034-1040, 1986). A pair of 9-BSb plus a pair of 9-BLa chromosomes is equal to a pair of standard chromosome 9's plus a duplication (4 doses) of a central region of chromosome 9. Proximal duplication stocks are useful in the construction of telocentric chromosomes (Zheng and Carlson, MNL 70: 28) and may be useful in studies on gene duplication.

Following the same procedures as Carlson and Curtis, the proximal duplication stocks for chromosomes 4 and 10 were constructed. For chromosome 4, TB-4Sa and TB-4Lb were combined into a 4-BSa 4-BSa 4-BLb 4-BLb stock (Figure 1). For chromosome 10, TB-10Sc and TB-10Lb were combined to produce a 10-BSc 10-BSc 10-BLb 10-BLb stock.

Evidence for successful production of proximal duplication 4 was found in mitotic root tips from the presumed homozygous stock. Fifteen seeds of this stock were examined cytologically. All 15 had 22 chromosomes without any telocentric (B-4) chromosomes (Figure 2A), as expected. Similarly, root tips from fifteen seeds of a putative homozygous stock of proximal duplication 10 were examined. All showed 22 chromosomes without any telocentric (B-10) chromosomes (Figure 2B).

Cytological examination of meiotic cells of plants with proximal duplication 4 showed the presence of a 4-BSa bivalent and a 4-BLb bivalent (Figure 2C). Proximal duplication 10 was also identified in meiotic cells. Bivalents of 10-BSc and 10-BLb were observed (Figure 2D). The structures of these chromosomes are consistent with those described by Beckett (J. Heredity 69:27-36,1978). Thus far, four proximal duplication stocks have been constructed, including those for chromosomes 3 and 9 (Carlson and Curtis) and chromosomes 4 and 10.

Figure 1. Construction of proximal duplication 4 by a series of crosses.

Figure 2. Proximal duplication stocks 4 and 10. A. 22 chromosomes in mitotic cell of proximal duplication 4. B. 22 chromosomes of proximal duplication 10. C. Pachytene stage of PD 4. D. Pachytene stage of PD10. Arrowheads indicate the centromeres of 4 and 10. 

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