250
B. L. ASTAUROV
while, when taking mutation chocolate (c/i) as a recessive marker, we
find besides black and brown first instar larvae some proportion of black
and brown bilateral "harlequins" or more complex irregular mosaics.
When some character manifested at more advanced stages of ontogenesis
is taken as a marker, it is easy to see that the recessive part of the body
is always of the male sex, while the dominant part can be of the male
or female sex with equal probability.
The highest percentage of such mosaic individuals is found when heat
shock begins at the critical stage of the second metaphase, or slightly
later. There can hardly be any other explanation for such cases than the
simultaneous cleavage of two diploid nuclei, one of them, zygotic, resulting as an amphimictic product of normal fertilization, the other arising
androgenetically by means of automictic fusion of two sperm nuclei.
Taking into account the frequency of appearance of different mosaic
types, it is possible to draw some conclusions concerning the regularities
of cleavage (Katsuki and Akiyama, 1927; Tazima, 1939, 1947, 1964).
It is necessary to add a few words about a recent attempt to interpret
all the data concerning thermal androgenesis and androzygotic mosaics
in the silkworm in a quite different way. Under the strong influence of
Lysenko's prejudice against "formal genetics" and his attitude towards
the leading role of environmental conditions in heredity, Sarkisian (1957)
and his collaborator Sarkisov (1959a,b, 1960) advanced a new explanation of "fatherlike" individuals (i.e., the androgenetic progeny and frequent cases of mosaicism with partly patroclinous, partly matroclinous
parts of the body). According to these authors, "fatherlike" specimens
or body regions appear as a result of a gradual oppression of the morphogenetic role of the maternal cytoplasm by sublethal temperature
conditions, in contrast to the unrestricted morphogenetic influence of the
more resistant paternal sex cells. These papers completely ignore all the
convincing cytogenetic evidence concerning the origin of androgenetic
males and different andro/zygotic mosaics, and deserve only a brief
mention.
VII. In Place of a Conclusion
As has been already emphasized in the introduction (Section II,A)>
the cytogenetic developmental mechanism acting at the conventional
starting point of silkworm ontogenesis can undergo surprisingly many
and surprisingly radical alterations which are nevertheless quite consistent with the typical pattern and successful progress of subsequent
morphogenesis.
Table III summarizes all previously recorded data and gives an idea
of the variety of cytogenetic developmental mechanisms already experimentally realized in the mulberry silkworm. There are not less than 17
B. L. ASTAUROV
while, when taking mutation chocolate (c/i) as a recessive marker, we
find besides black and brown first instar larvae some proportion of black
and brown bilateral "harlequins" or more complex irregular mosaics.
When some character manifested at more advanced stages of ontogenesis
is taken as a marker, it is easy to see that the recessive part of the body
is always of the male sex, while the dominant part can be of the male
or female sex with equal probability.
The highest percentage of such mosaic individuals is found when heat
shock begins at the critical stage of the second metaphase, or slightly
later. There can hardly be any other explanation for such cases than the
simultaneous cleavage of two diploid nuclei, one of them, zygotic, resulting as an amphimictic product of normal fertilization, the other arising
androgenetically by means of automictic fusion of two sperm nuclei.
Taking into account the frequency of appearance of different mosaic
types, it is possible to draw some conclusions concerning the regularities
of cleavage (Katsuki and Akiyama, 1927; Tazima, 1939, 1947, 1964).
It is necessary to add a few words about a recent attempt to interpret
all the data concerning thermal androgenesis and androzygotic mosaics
in the silkworm in a quite different way. Under the strong influence of
Lysenko's prejudice against "formal genetics" and his attitude towards
the leading role of environmental conditions in heredity, Sarkisian (1957)
and his collaborator Sarkisov (1959a,b, 1960) advanced a new explanation of "fatherlike" individuals (i.e., the androgenetic progeny and frequent cases of mosaicism with partly patroclinous, partly matroclinous
parts of the body). According to these authors, "fatherlike" specimens
or body regions appear as a result of a gradual oppression of the morphogenetic role of the maternal cytoplasm by sublethal temperature
conditions, in contrast to the unrestricted morphogenetic influence of the
more resistant paternal sex cells. These papers completely ignore all the
convincing cytogenetic evidence concerning the origin of androgenetic
males and different andro/zygotic mosaics, and deserve only a brief
mention.
VII. In Place of a Conclusion
As has been already emphasized in the introduction (Section II,A)>
the cytogenetic developmental mechanism acting at the conventional
starting point of silkworm ontogenesis can undergo surprisingly many
and surprisingly radical alterations which are nevertheless quite consistent with the typical pattern and successful progress of subsequent
morphogenesis.
Table III summarizes all previously recorded data and gives an idea
of the variety of cytogenetic developmental mechanisms already experimentally realized in the mulberry silkworm. There are not less than 17