. The physical basis of heredity . Oocyte ?• Polar Spmdle 2^^ Polar Spindle ^p ^^f^^ Polav Bodies Fig. 26.—Reduced chromosome group; and extrusion of polar bodies in Protcnor. Maturation Divisions or Proteimor d o o Melaphas? oj the1 ^ Spermatocyte. W^oJ Anaphase o| theP Spermatocyte Metapbse oj the2^SpGnnaIoi;yte t£Qc:> I In; j] Anaphase o\ the oi,a c * Spermatozoa / opermatocyt? ^ Fro. 27.—Reduced chromosome group of male; and spermatogenesis in Protenor. the fused pairs show that these two large chromosomesmust always unite with each other (Fig. 26), In themale of certain species, as in
. The physical basis of heredity . Oocyte ?• Polar Spmdle 2^^ Polar Spindle ^p ^^f^^ Polav Bodies Fig. 26.—Reduced chromosome group; and extrusion of polar bodies in Protcnor. Maturation Divisions or Proteimor d o o Melaphas? oj the1 ^ Spermatocyte. W^oJ Anaphase o| theP Spermatocyte Metapbse oj the2^SpGnnaIoi;yte t£Qc:> I In; j] Anaphase o\ the oi,a c * Spermatozoa / opermatocyt? ^ Fro. 27.—Reduced chromosome group of male; and spermatogenesis in Protenor. the fused pairs show that these two large chromosomesmust always unite with each other (Fig. 26), In themale of certain species, as in Protenor (Fig. 27), the MECHANISM IN SEGREaATION 57 sex chromosome has no mate, and therefore nothing tofuse with. Its size, after the others have conjugated(Fig. 27) shows that it remains single; while its failureto divide twice, as do the other chromosomes, corrobo-rates the view that having no mate of its own it nevercombines with any other. At the other extreme, the twovery minute chromosomes in several of the Drosophilaspecies must have united to form the smallest chromo-some of the reduced series (Fig. 28, a-a, h-b). In afew cases the X and the Y are different in size. Whenthey fuse (in the male) the size of the fused mass is what I
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectheredit, bookyear1919
