The behaviour of two modifiers inDrosophila obscura, m 1, located in theX-chromosome at 13·7 units fromP I andm 2, linked with orange in the third linkage group and located at 9·2 units from orange, is described.
PII, an allelomorph of the previously described Pointed (PI) mutant, gives a similar but weaker effect upon the wing character to Pointed.
The genem 1, which has the effect of intensifying the character, gives a weaker effect withP II than withP I. The genem 2, which reduces the variability of the character, similarly affectsP II less thanP I.
It is suggested thatP I andP II inD. obscura are homologous withBd (Beaded) inD. melanogaster because of (a) the great similarity of the morphological expression of the two genes, and (b) the similarity of their behaviour in the presence of modifying factors.
A tentative suggestion is put forward to explain the autosomal position of Beaded as compared with the sex-linked nature ofP I andP II. It is suggested that as the result of translocation theX-chromosome inD. obscura has one arm, or part of one arm, corresponding to part of the third chromosome inD. melanogaster. This hypothesis is supported by (a) the cytological differences in size and shape of theX-chromosomes inD. obscura andD. melanogaster, (b) by the position of the yellow-scute loci in the two species, (c) by the evidence from the hybrids between raceA andB ofD. obscura, and (d) the cytological observations of similar rearrangement of chromosome parts in many plants and inDrosophila melanogaster.
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Koller, P.C. “Pointed,” and the constitution ofX-chromosome inDrosophila obscura . Journ. of Genetics 26, 215–229 (1932). https://doi.org/10.1007/BF02984690
- Linkage Group
- Yellow Gene
- Chromosome Part
- Plate XVII
- Similar Rearrangement