THE LINKAGE DISTURBANCE INVOLVED IN THE 



CHROMOSOME TRANSLOCATION I. OF DROSO- 



PHILA, AND ITS PROBABLE SIGNIFICANCE. 



G. W. DELUZ HAMLETT, 

 DEPARTMENT OF ZOOLOGY, UNIVERSITY OF TEXAS. 



The chromosomal abnormality in Drosophila known as "trans- 

 location I." was found by Bridges in 1917, and was first referred 

 to by Morgan (1919); a preliminary account of it was given by 

 Bridges in 1923. The case is a very remarkable one, unique in 

 the literature to date, and it raises certain new problems con- 

 cerning the arrangement which genes may have in a chromosome 

 as well as concerning the changes in arrangement which they 

 may undergo. The abnormality arose by a portion of the right 

 hand end of chromosome II. breaking off and becoming attached 

 near the middle of the right half of chromosome III. Bridges' 

 data showed the size of the transposed piece and its approximate 

 point of attachment on the third chromosome. It was known 

 that the break in chromosome II. was between arc (ar) and 

 plexus (pi), making the fragment about 8 units long, and that 

 the transposed piece was attached somewhere between ebony (e) 

 and rough (ro) in chromosome III. The deficient second chromo- 

 some was known as "Pale," from its effect on eosin-eyed flies, 

 and the deficiency was lethal unless accompanied by trans- 

 location. 



In the hope of getting further light on the chromosome change 

 involved, the writer undertook to test more extensively the third 

 chromosome linkage values in flies which carried the trans- 

 location. I wish to take this opportunity to express my in- 

 debtedness to Dr. H. J. Muller, who suggested the work, and 

 whose aid and suggestions have made it possible. In these 

 experiments the homozygous as well as the heterozygous condition 

 of translocation was studied, and all of the left hand end of 

 Chromosome III. was under genetic observation. Bridges had 

 already shown that crossing over was greatly reduced in the 

 region close to the locus of translocation ; but his data included 



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