The summed lengths of chromosomes Nos. 1 and 2 (x) were compared with the summed lengths of the small acrocentric chromosomes, Nos. 21, 22 and in males the Y chromosome (z), in 10 cells from each of 10 males and 5 females. Both chromosome groups varied in length together, but the changes were proportionally less in the small acrocentric chromosomes than in the large chromosomes. This was the case in both sexes. The relative changes in chromosome length were expressed by the regression coefficients z = 0.1461 x + 5.55 in males and z = 0.1077x + 4.32 in females. It was considered that this differential contraction might be peculiar to the stage of chromosome contraction examined and that compensatory contraction occurred at other stages, or, on the other hand, that the greater degree of contraction of the large chromosomes involved an additional order of chromosome coiling.
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