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
239
A much more serious obstacle to polyploidy in bisexually reproducing
animals consists in the sterility of the homogametic sex. Fertility of 312
male silkworms has been studied during the first four generations of a
bisexual allotetraploid strain (Vereiskaya and Astaurov, 1965). Unfortunately, their fertility does not improve despite selection working during
the reproduction of the strain. Although the highest percentage of hatching attained in one of the batches is 72%, the mean percentage of
hatching larvae in crosses with tetraploid males amounts only to 0.6%
per batch.
Fairly good progress in the field of animal amphiploidy has been
made by Kawamura and his co-workers (Kawamura and Nishioka,
1960, 1963; Kawamura et al, 1963; Nishioka, 1963). Recently, several
veritable amphidiploids were produced in this laboratory between closely
related species of Anura, Rana japonica ornativentris X Rana nigromaculata brevipoda. However, even in these cases the inter se reproduction of tetraploids has not so far been accomplished.
Diploid interspecific hybrids can be obtained between many quite
distinctive "good" species and even different genera of animals. Some of
these hybrids, belonging to the highest orders of Metazoa, such as Lepidoptera, Coleoptera, Hymenoptera, and Diptera among the insects and
Aves and Mammalia among the vertebrates are quite sterile. Unreduced
gametes and triploid progeny were obtained in some Lepidoptera interspecific hybrids (Federley, 1928, 1953), and it seems possible that genuine fertile amphidiploids can be obtained in such cases.
The possibility of overcoming hybrid sterility and reproductive isolation in animals by applying the same basic principle of amphidiploidy
which has been previously found as effective in plants by Karpetchenko
and Müntzing seems to be of some general interest.
VI. Alterations of the Cytogenetic Mechanism of Maturation and
Fertilization in the Just-Inseminated Egg
So far we have considered different alterations of the cytogenetic
mechanism of maturation in unfertilized oocytes and their developmental
consequences. Let us turn now to the alterations which can be obtained
just after insemination.
A. Diploid Gynogenesis
Elimination of the sperm nucleus (or nuclei in case of physiological
polyspermy) prior to caryogamy leads to a particular, kind of parthenogenesis which, for the sake of discrimination, is denoted as gynogenesis.
The activation reaction of an oocyte stimulated by the penetrating
spermatozoon (or spermatozoa) develops at first via normal maturation
239
A much more serious obstacle to polyploidy in bisexually reproducing
animals consists in the sterility of the homogametic sex. Fertility of 312
male silkworms has been studied during the first four generations of a
bisexual allotetraploid strain (Vereiskaya and Astaurov, 1965). Unfortunately, their fertility does not improve despite selection working during
the reproduction of the strain. Although the highest percentage of hatching attained in one of the batches is 72%, the mean percentage of
hatching larvae in crosses with tetraploid males amounts only to 0.6%
per batch.
Fairly good progress in the field of animal amphiploidy has been
made by Kawamura and his co-workers (Kawamura and Nishioka,
1960, 1963; Kawamura et al, 1963; Nishioka, 1963). Recently, several
veritable amphidiploids were produced in this laboratory between closely
related species of Anura, Rana japonica ornativentris X Rana nigromaculata brevipoda. However, even in these cases the inter se reproduction of tetraploids has not so far been accomplished.
Diploid interspecific hybrids can be obtained between many quite
distinctive "good" species and even different genera of animals. Some of
these hybrids, belonging to the highest orders of Metazoa, such as Lepidoptera, Coleoptera, Hymenoptera, and Diptera among the insects and
Aves and Mammalia among the vertebrates are quite sterile. Unreduced
gametes and triploid progeny were obtained in some Lepidoptera interspecific hybrids (Federley, 1928, 1953), and it seems possible that genuine fertile amphidiploids can be obtained in such cases.
The possibility of overcoming hybrid sterility and reproductive isolation in animals by applying the same basic principle of amphidiploidy
which has been previously found as effective in plants by Karpetchenko
and Müntzing seems to be of some general interest.
VI. Alterations of the Cytogenetic Mechanism of Maturation and
Fertilization in the Just-Inseminated Egg
So far we have considered different alterations of the cytogenetic
mechanism of maturation in unfertilized oocytes and their developmental
consequences. Let us turn now to the alterations which can be obtained
just after insemination.
A. Diploid Gynogenesis
Elimination of the sperm nucleus (or nuclei in case of physiological
polyspermy) prior to caryogamy leads to a particular, kind of parthenogenesis which, for the sake of discrimination, is denoted as gynogenesis.
The activation reaction of an oocyte stimulated by the penetrating
spermatozoon (or spermatozoa) develops at first via normal maturation