File:Analysis of development (1955) (18171004601).jpg

Title: Analysis of development
Identifier: analysisofdevelo00will (find matches)
Year: 1955 (1950s)
Authors: Willier, Benjamin H. (Benjamin Harrison), b. 1890
Subjects: Embryology; Embryology
Publisher: Philadelphia, Saunders
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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Fig. 34. Development of dispermic sea urchin egg. a. Fusion of both sperm nuclei with egg nucleus, each containing a haploid set of 18 chromosomes; both sperm asters have divided, h. Random distribution of 54 chromosomes among spindles connecting the four poles of the mitotic figure, c. Anaphase; chromosomes from two adjacent spindles move toward each pole, d. Telophase; division of egg into four cells with different numbers of chromosomes, e, "Stereoblastula," final stage of development. Cells of right-hand half disinte- grating. (After Boveri, '07.) Haploid/diploid mosaics are easily dis- covered among the offspring of crosses be- tween white and dark axolotls, if the haploid area is derived from the white (recessive) parent. Figure 33« shows an unusually regu- lar lateral mosaic of this type with a sharp line of demarkation almost exactly in the median plane. The organs on the haploid (left) side are smaller than those on the right. Dissection of the animal at the age of eight months further revealed that this in- dividual started out as a gynandromorph, with a testis on the left and an ovary on the right side. However, at the time of the autopsy the ovary had been almost com- pletely transformed into a testis under the influence of the male sex hormone produced by the testis on the haploid side. The origin of this lateral mosaic may be explained in either one of two ways which are described in Figures 336 and c. sis between haploid and diploid embryos of T. pyrrhogaster, which also accomplishes a joint circulation, did not result in the ex- pected improvement of the haploid partner, aside from a reduction of the edema (Kaylor, '40). The presence of a partly diploid nervous system may be another factor favoring nor- mal functioning of the haploid side of the body. Finally, the proximity of normal dip- loid tissues may have a stimulating influence on adjacent haploid tissues, as has been shown by Hadorn ('35, '37) in chimaeras composed of halves of diploid and haploid embryos. The Effects of Irregular Distribution of Chromosomes in Multipolar Mitosis. In sea urchin eggs that are fertilized by two sper- matozoa, both sperm nuclei fuse with the egg nucleus (Fig. 34a) so that three sets of chromosomes are present at the first division of the egg. In the majority of such eggs, both

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