Biology Pamphlets Volume 1858

Biology Pamphlets Volume 1858

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...phenomena. In this case, both parents were undoubtedly homozygous for their respective endosperm characters, so that heterozygosity will not account satisfactorily for the deviations. But this is a different phenomena than Swingle found in his Citrus hybrids, for here one is dealing with a fluctuation in a proportion or ratio involving the same character, while in his experiments the difficulty was the variation in presence and absence of distinct and often new characters, indicating an extremely heterozygous parentage. As an explanation or working hypothesis for his own and similar data, Swingle advances a somewhat new and suggestive chromosome theory on the assumption that it fills an urgent need. The theory of zygotaxis, as it is called, may be summarized as follows: Maternal and paternal chromosomes probably persist side by side in the cells, unchanged in quality and number throughout the whole development of the F1 organism. This being true, Swingle, in order to explain his data, assumes that the influence in character formation exerted by chromosomes on the F, hybrids, is in some cases due to their relative positions in the nucleus, and that these relative positions result from accident or at least are determined at the moment of nuclear fusion in fertilization, and remain unchanged in succeeding cell generations. He further assumes that those chromosomes lying nearest the nuclear wall (peripheral) are better nourished than those centrally located, and hence they exert more influence in character formation, and dominating synapsis, produce gametes similar in their hereditary character to the cells of the first generation hybrids, whose character in turn was determined at fertilization by the configuration the chromosomes took in the more

Product details

  • Paperback | 30 pages
  • 189 x 246 x 2mm | 73g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236516397
  • 9781236516398