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Fig. 9-11. Chromosome and chromatid breaks in Drosophila melanogaster. Dia- 

 grams showing positions of breaks in nine rearrangements having duplicated sections 

 in one of the chromosomes represented. The chromosomes (2L, 2R, 3L, 3R, X, 4) 

 are diagramed in the two-strand stage; centromeres are shown at left. Approximate 

 positions of breaks are indicated by gaps, the chromosome type occurring at the 

 same level in both strands, the chromatid type represented in only one strand. Por- 

 tions of the chromosomes that were identified in the salivary-gland nuclei are repre- 

 sented in solid color; portions not recovered, in cross hatching. The rearrangement 

 indicated in (a) appeared as a mosaic, some nuclei of the salivary gland showing a 

 duplication of the reversed-repeat type, other nuclei showing a deficiency resulting 

 from recombination of the stippled parts of the chromosome. When chromosomes 

 other than those showing the duplicated sections were involved in a complex rear- 

 rangement, the positions of breaks in these chromosomes are also indicated. Thus, 

 in 0') duplicated sections of 2L were identified, but the rearrangement also involved 

 breaks in 2R, 3R, and the Y chromosome. The rearrangement diagramed in (d) 

 had 14 breaks, although only 12 are shown because the positions of the breaks in one 

 of two reversed repeats could not be identified. The rearrangement represented in 

 (g), which is a duplication for the entire length of 3R, was found in some cells of a 

 salivary gland but was lacking in others. 



649 



