The theory of the gene / by Thomas Hunt Morgan.

  • Morgan, Thomas Hunt, 1866-1945.
Date:
1926
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The theory of the gene / by Thomas Hunt Morgan. Source: Wellcome Collection.

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    THE MECHANISM OF HEREDITY 43 about each other (Fig. 28b), but this interpretation is often open to suspicion. It is extremely difficult, in fact, to determine when threads as delicate as these come into contact with each other whether they pass above or below, i.e., above at one node and below at the next, etc. The difficulty is enormously enhanced by the coagulated con¬ dition of the threads, and it is only in this condition that they are stained for microscopic study. Conjugation of a pair of chromosomes of a planarian. In a, the two thin threads are coming together; in b, there are indications, at two levels, of crossing-over of the two united strands. (After Gelei.) The preparations that most nearly approach a demon¬ stration of the twisting of the leptotene threads are those in which the conjugation begins at one end (or at both ends of bent chromosomes) and progresses toward the other end (or toward the middle of the bend). The sperm- cells of Batrachoseps presents perhaps the most seduc¬ tive preparations of this sort (Fig. 26), but the figures of Tomopteris are almost or quite as good. The drawings Fig. 28.