Singleness or Doubleness of the Chromosomes in the Successive Stages of Mitosis

Afify, Alaa M

doi:10.1508/cytologia.9.319

Cited by 2 publications

(1 citation statement)

References 37 publications

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“…As indicated in Table II anaphase somatic chromosomes are considered by many to contain a single spiral (also by Belar, 1929;Belling, 1933;Gustafsson, 1936;Darlington, 1937, p.33;Mather, 193? ;White, 1937;Afify, 1938) rather than two loosely interwoven chromonemata. However, in some cases {Smith, 1932{Smith, , 1934Geitler, 1935Geitler, , 1938Sax and Sax, 1.935;lv1ensinkai, 1939;Colernan, 1940 a and b) it is considered that an apparently single spiral may actually be composed of two or more closely appressed chromonemata, which may not appear visibly <listinct until telophase or the following prophase.…”

Section: Theories Of Spiralizationmentioning

confidence: 99%

STUDIES ON THE CHROMOSOME SPIRALIZATION CYCLE INTRILLIUM

Sparrow¹,

Huskins²,

Wilson³

1941

Can. J. Res.

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Studies of the major, relic, and relational coils and of chromosome, chromatid, and chromonema length changes in meiotic, microspore, and root tip chromosomes of Trillium erectum L. and T. grandiflorum Salisb. have led to the following conclusions:—Elongation of the chromonema occurs between early diakinesis and first anaphase and between second anaphase and microspore prophase. Contraction occurs between zygotene and early diakinesis, between first and second anaphase, and during microspore prophase. Chromonema elongation between early diakinesis and anaphase is associated with the formation of the major coil and its transition into the relic coil of the microspore prophase is accompanied by a further elongation. The tertiary split results in the half-chromatids being associated in the form of a plectonemic spiral, which persists as such to microspore prophase. The gyres of the plectonemic relic coil become partially straightened out to form a relational coil, whose twists are in the same direction as their antecedent relic coils. During microspore prophase some relational twists are apparently eliminated at intrabrachial changes of direction, others by contraction and untwisting of the chromatids.Changes of direction fall into three categories: (1) those associated with attachments, (2) those associated with chiasmata, and (3) the remainder, the frequency of which is proportional to the number of gyres. Intrabrachial changes of direction are more numerous in microspore prophase than in root tip chromosomes, presumably because Factor (2) is inoperative in the latter. There are very few data that could possibly be taken to indicate that chromosomes may have an inherent directional pattern of coiling.To the tentative hypothesis of Wilson and Huskins that the major coil of meiosis is formed by an elongation of the chromonema within a restricted space, the pellicle, the following may be added: the half-chromatids at metaphase are wound in the form of a plectonemic spiral. The straightening out of this spiral results in the relationally twisted chromatids of microspore prophase. These twists are eliminated both by cancellation at the points at which changes of direction have occurred in the major coil and also by contraction and untwisting of the chromatids.

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