Location of orp1 on chromosome 4S demonstrates a useful aspect of the selfed-hypoploid test for locating duplicate factors. If mutant alleles of both members of the duplicate pair are present in an ear stock and are crossed by both short arm and long arm B-A translocations for the chromosome on which one member of the pair is located, then depending upon whether the mutant tested is (1) distal to the breakpoint on the short arm; (2) between the breakpoints on both arms; or (3) distal to the long arm breakpoints, the following types, as reflected by normal to orange ratios, should occur.
The diagnostic ratios are: 1) 3:1 ratios for all the segregating hypoploid selfs, which place the mutant on the correct chromosome; 2) 15:1 ratios for all the segregating hyperploid selfs for both translocations, which would place the mutant between the breakpoints of both arms; and (3) the 60:1 vs. the 15:1 ratios for the segregating hyperploid selfs of the respective B-A translocation, which would place the mutant on the correct arm.
M.G. Neuffer and J.B. Beckett
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