Physical mapping of RFLPs on the long arm of chromosome 10 (10L) by terminal deficiencies (TDs) induced by the r-X1 deletion reveals a difference between the physical and genetic maps (Lin et al., Mol. Gen. Genet. 256:509-516, 1997). In the former, bnl10.13 and bnl17.02 are distal to bnl7.49, but, in the latter, they are proximal. This difference can be due to an incorrect placement of the first two RFLPs on either the genetic map or the physical one.

These two possibilities can be distinguished by studying the r-X1 deletion according to the following rationale: the physical position of bnl10.13 and bnl17.02 has been determined by two TDs on 10L generated by the r-X1 deletion. The two RFLPs fail to give the maternal signal on the two TDs, but bnl7.49 does, indicating the former being distal to the latter. Alternatively, since the two TDs carry a terminal deficiency as well as the r-X1 deletion, bnl10.13 and bnl17.02 may be located in the latter. In other words, their maternal signal being absent on the two TDs is the result of their being deleted from the r-X1 deletion, not from the terminal deficiency. This supposition can be substantiated by studying a 10L that carries the r-X1 deletion but not a terminal deficiency, that is, the r-X1-carrying chromosome 10. To do this, the r- X1/R-r (W22) was pollinated by an r-g tester, and the resulting colorless kernels, carrying the r-X1 deletion, are compared with the colored ones, carrying a normal chromosome 10. The maternal signal of bnl10.13 and bnl17.02 was not observed in the former, but it was in the latter, indicating that the two RFLPs are indeed located in the r-X1 deletion. As a consequence, the physical map of 10L is consistent with its genetic map.

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