C Y T O G E N E T I C M E C H A N I S M S I N S I L K W O R M S
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alterations in the normal cytogenetic processes of maturation and fertilization are quite consistent with a typical and successful course of
morphogenesis.
The predetermination just mentioned may serve as rather a plausible
explanation of this stability of morphogenesis under various seemingly
serious disturbances of the normal mode of reproduction. Prior to cleavage, however, the egg may be considered to be simultaneously a cell, a
gamete (or a zygote), and a germ; all events occurring at this conventional starting point of development are consequently not only of
cytologie and genetic, but also of profound morphogenetic significance.
Certain cytogenetic processes which ensure the transformation of the preembryonic (maternal) genetic constitution into the definitive filial one
provide the newly arising individual with the necessary genetic information for the rest of ontogenesis. This information concerns not only minor
hereditary peculiarities, but it is decisive for the fate of the developing
individual with respect to such important genetic characteristics as
its homozygosity or heterozygosity, sexual chromosome constitution,
ploidy, etc.
Artificial means for the induction of certain modifications of cytogenetic reproductive mechanisms may consequently serve as a tool for
the efficient control of such important characters of the progeny as sex
and ploidy.
Special experimental designs, such as heterospermic androgenesis (Astaurov and Ostriakova-Varshaver, 1957a-c) made it possible to compare
the relative morphogenetic role of nuclear and extranuclear patterns in
the embryo.
There exist several extensive and detailed reviews concerning alterations of the cytogenetic mechanism of reproduction and early development of animals (Peacock and Weidmann, 1961, 1964; White, 1954;
Narbel-Hofstetter, 1964). Some of these reviews have been written
comparatively recently; they are dedicated mostly to alterations connected with parthenogenesis, gynogenesis, and polyploidy, but none of
them deals with experimentally produced alterations. Data drawn from
Lepidoptera play for instance, a rather conspicuous role in these reviews,
yet important experimental results obtained in Bombyx mori are completely omitted. The unique experimental plasticity of the cytogenetic
mechanism of development in the mulberry silkworm deserves special
attention. It is difficult to say whether this plasticity is simply a result
of extensive experimentation with an economically useful insect, or a
rare specific peculiarity, but surely there is no other experimental animal
whose reproduction and development can successfully proceed in such
diverse ways.
This may serve as a sufficient justification for the fact that cytogenetic
201
alterations in the normal cytogenetic processes of maturation and fertilization are quite consistent with a typical and successful course of
morphogenesis.
The predetermination just mentioned may serve as rather a plausible
explanation of this stability of morphogenesis under various seemingly
serious disturbances of the normal mode of reproduction. Prior to cleavage, however, the egg may be considered to be simultaneously a cell, a
gamete (or a zygote), and a germ; all events occurring at this conventional starting point of development are consequently not only of
cytologie and genetic, but also of profound morphogenetic significance.
Certain cytogenetic processes which ensure the transformation of the preembryonic (maternal) genetic constitution into the definitive filial one
provide the newly arising individual with the necessary genetic information for the rest of ontogenesis. This information concerns not only minor
hereditary peculiarities, but it is decisive for the fate of the developing
individual with respect to such important genetic characteristics as
its homozygosity or heterozygosity, sexual chromosome constitution,
ploidy, etc.
Artificial means for the induction of certain modifications of cytogenetic reproductive mechanisms may consequently serve as a tool for
the efficient control of such important characters of the progeny as sex
and ploidy.
Special experimental designs, such as heterospermic androgenesis (Astaurov and Ostriakova-Varshaver, 1957a-c) made it possible to compare
the relative morphogenetic role of nuclear and extranuclear patterns in
the embryo.
There exist several extensive and detailed reviews concerning alterations of the cytogenetic mechanism of reproduction and early development of animals (Peacock and Weidmann, 1961, 1964; White, 1954;
Narbel-Hofstetter, 1964). Some of these reviews have been written
comparatively recently; they are dedicated mostly to alterations connected with parthenogenesis, gynogenesis, and polyploidy, but none of
them deals with experimentally produced alterations. Data drawn from
Lepidoptera play for instance, a rather conspicuous role in these reviews,
yet important experimental results obtained in Bombyx mori are completely omitted. The unique experimental plasticity of the cytogenetic
mechanism of development in the mulberry silkworm deserves special
attention. It is difficult to say whether this plasticity is simply a result
of extensive experimentation with an economically useful insect, or a
rare specific peculiarity, but surely there is no other experimental animal
whose reproduction and development can successfully proceed in such
diverse ways.
This may serve as a sufficient justification for the fact that cytogenetic