. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. Fig. 28.—Diagram of mitosis in a species having four chromosomes in its cells. A, The "resting" cell. B, Formation of the spireme-thread. C, Longitudinal division of the spirome-thread and transverse segmentation into four chromosomes. D, Separation of the daughter chromosomes formed by longitudional splitting of spireme-thread. E, Beginnings of nuclear reconstruction and division of the cell body. F, Cell division complete and daughter nuclei in the "resting" stage. organized i
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. Fig. 28.—Diagram of mitosis in a species having four chromosomes in its cells. A, The "resting" cell. B, Formation of the spireme-thread. C, Longitudinal division of the spirome-thread and transverse segmentation into four chromosomes. D, Separation of the daughter chromosomes formed by longitudional splitting of spireme-thread. E, Beginnings of nuclear reconstruction and division of the cell body. F, Cell division complete and daughter nuclei in the "resting" stage. organized into threads of chromomeres which pair as shown at B. In this diagram the paired threads are taken to represent homologous chromo- somes, and the opposite chromomeres in a pair of threads are considered as the homologous chromomeres of the two chromosomes. The paired threads contract and fuse along their entire length giving the figure diagrammed at C in which the two loops represent two pairs of homolo- gous chromosomes in the conjugation stage, the essential step in sj'nap- sis. Following this stage the two contracted loops of chromatin split lengthwise and unravel in somewhat the manner shown in D. These filaments contract again forming the intertwined pairs of chromosomes shown at E, and the nuclear membrane thereupon begins to disappear. Further contraction and the formation of a spindle results in the reduc- Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Babcock, E. B. (Ernest Brown), b. 1877; Clausen, Roy Elwood, 1891-. New York, McGraw-Hill; [etc. , etc. ]
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