. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 274 SALLY HUGHES-SCHRADER regions appear to lie in the same plane, but as the tension in the kinetochore loop increases they may assume alternating planes (Fig. 6, middle left bivalent). The chromatids of each chromosome have not yet separated, and even the line of demarcation between chromosomes cannot be followed in the closely paired regions. It is thus impossible to determine whether or not chiasmata are present in the persistently paired regions. At the stage of maximum stretch, however, open cross formations are freque
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 274 SALLY HUGHES-SCHRADER regions appear to lie in the same plane, but as the tension in the kinetochore loop increases they may assume alternating planes (Fig. 6, middle left bivalent). The chromatids of each chromosome have not yet separated, and even the line of demarcation between chromosomes cannot be followed in the closely paired regions. It is thus impossible to determine whether or not chiasmata are present in the persistently paired regions. At the stage of maximum stretch, however, open cross formations are frequently encountered either at one end of a bivalent, giving the rod-shaped configuration, or at both with a resulting ring configuration (Fig. 8). In these bivalents it is clear that non-sister chromatids are associated distal to the opening of the cross. No open cross configurations have been found in the sex trivalent. There is thus no evidence available as to whether or not the terminal adhesions of Xi, Y, and Xo are of chiasmatal origin. The final form of the bivalents at completed metaphase is fairly constant (Fig. 11). The most frequent complement comprises three rings and nine rods;. FIGURE 11. Stagmomantis Carolina, Virginia. Bivalents and sex trivalent at metaphase. Gentian violet. rings vary in number from none to four per nucleus—rods show the corresponding range of 12 to eight. The open cross may persist to metaphase in from one to four bivalents, but the terminal connection is more commonly a swelling or lump, sometimes bipartite. Stagmomantis Carolina from Barro Colorado Island Taxonomically indistinguishable, Stagmomantis Carolina males from Barro Colorado Island and from Virginia are also identical in chromosome complement as observed in spermatogonial and meiotic metaphases. Striking and constant differences, however, characterize the meiotic prophase in the two types. In the Barro Colorado material the pachytene polarization is initiated always at a later stage
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
