The results reported in this note were obtained to establish whether the duplicated segments Dp 10-1, -3 and -4, lying in the long arm of chromosome 10 (Gavazzi, 1975, Heredity 35:389) are terminal or interstitial. Genetic markers used in testcrosses of the heterozygotes diagrammed here are R and o7 lying at positions 57 and 80 respectively on the long arm of chromosome 10:
As outlined in this scheme r-g + crossovers recovered
in testcrosses of (A) parents should carry the duplicate segment while
only a fraction of the crossover strands should carry it if the duplication
is not terminal. Presence of the duplication was inferred from the development
of anthocyanin in the sporophytic tissues since the Dp segment carries
the P component of the R locus. The results are given here below:
| N | Dp | |
| Dp 10-1 | 2 | 49 |
| Dp 10-3 | 0 | 112 |
| Dp 10-4 | 0 | 7 |
These data, referring to the distribution of the Dp segment among verified r-g + crossover strands recovered in the progeny of heterozygous parents with an r-g o7 homozygous tester, are taken as evidence that all three duplications tested are terminal.
Giuseppe Gavazzi
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