. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. A STUDY OF CHROMOSOME ENDS 161 occur with an unaltered frequency, others are encountered much more often, and notably 3L-3R which soars from 6 per cent to 24 per cent. The indications seem to be that 3L and 3R, since they remain structurally unaltered, had the ability to adhere in the Ore'R strain but this was never realized due to a stronger attraction between X and 3R. In other words, once the stronger attraction is eliminated by bringing in a foreign X, the weaker attraction becomes the strongest remaining. (The word &quo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. A STUDY OF CHROMOSOME ENDS 161 occur with an unaltered frequency, others are encountered much more often, and notably 3L-3R which soars from 6 per cent to 24 per cent. The indications seem to be that 3L and 3R, since they remain structurally unaltered, had the ability to adhere in the Ore'R strain but this was never realized due to a stronger attraction between X and 3R. In other words, once the stronger attraction is eliminated by bringing in a foreign X, the weaker attraction becomes the strongest remaining. (The word "attraction" is used throughout in a purely descriptive sense and in no way is an attempt made to imply physical forces.) Thus, by substituting a foreign X chromosome and a foreign X chromosome tip into the Ore' R strain, the locus of specificity involved in terminal adhesion is found to be the end of the chromosome. The experiment also reveals unsuspected. ri ! uiryl- i i IIK .•A » ' I * li;'\'; sSi III) «rj bis,/.. FIGURE 4. The distal end of the X chromosome in: a. Oregon-R. b. Swedish-b. c. Swedish-b on Oregon-R base. d. Marker stock. potential attractions carried by the chromosome ends—attractions which result in adhesions only in the absence of stronger attractions. Cytological examination of the chromosome ends Detailed study was made of the banding at the end of the chromosome in the strain, the Ore'R strain, the tip on the Ore'R X base, and the marker stock used to obtain the crossovers (sc ec cv ct6 v s'-' f car bbl). This study demon- strated that the Ore'R and the marker stock X chromosomes are longer by a no- ticeable amount than either of the two X chromosomes. A study of Figure 4 shows that the Ore'R and marker X chromosomes have regions 1A 1-i (Bridges map) while the others lack this. Whether this is a typical terminal defi- ciency as described in connection with the micromanipulation data in a previous section of the present paper,
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
