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
243
This is the case without exception. Thus, exceptional individuals are
undoubtedly androgenic. (2) As shown by direct investigation, these
androgenetic males are always diploid and very often normally fertile.
Two possibilities are then equally conceivable: (a) Either the diploid
chromosome set of the androgenetic males has arisen from one sole
haploid spermatozoon by means of some kind of diploidization (monospermic, strictly homozygous diploid androgenesis), or (b) the diploid
complex has arisen by means of fusion of two different sperm nuclei
(dispermic, heterozygous diploid androgenesis).
This uncertainty was unquestionably settled by Hasimoto's work
(1934b), where the male parent was homozygous for mutation od and
was at the same time heterozygous for another character semidominant
Kp (supernumerary abdominal legs) and therefore produced 50% odKp
and 50% odkp spermatozoa.
In the first case (monospermic androgenesis), the ratio among exceptional androgenetic od individuals should be according to expectation
1 odod, KpKpil
odod, kpkp, while in the second case of dispermic
androgenesis the expectation is 1 odod, KpKp:2 odod, Kpkpil odod,
kpkp, as in the case of monohybrid F 2 segregation. The results obtained
are unquestionably in favor of dispermic androgenesis and heterozygous
Kpkp males phenotypically different from homozygous KpKp individuals
appeared in the expected quantity. This opens the possibility of producing bipaternal androgenesis, which has been realized by means of double
insemination of a sole female by two different males (Strunnikov, 1958).
A portion of androgenetic individuals inherits in such cases genetical
markers from both fathers, displaying a noticeable hybrid vigor; these
are Έ τ hybrids between two male parents, not forgetting their "third
parent," the "foster mother" that furnishes the androgenetic progeny
with their cytoplasmic organization and supply.
Androgenetic individuals are males without exception, while individuals obtained by means of heat parthenogenesis are always females.
Thus both methods, androgenesis and heat parthenogenesis, when combined might serve as a useful means for sex control in sericulture. Male
cocoons in Bombyx are richer in silk content than those of females, and
deliberate production of pure male offspring is especially desirable.
Unfortunately, the efficiency of heat androgenesis is still very low: (1)
Drastic heating of freshly fertilized eggs in the sensitive (critical) phase
(second prometaphase) which often results in androgenesis induces many
other nuclear and developmental abnormalities lethal for the great majority of embryos; and (2) with respect to the survivors, not all of them
develop along the androgenetic path; a fairly large proportion, in spite
of heat treatment, persist in normal zygotic development by way of
syngamy.
243
This is the case without exception. Thus, exceptional individuals are
undoubtedly androgenic. (2) As shown by direct investigation, these
androgenetic males are always diploid and very often normally fertile.
Two possibilities are then equally conceivable: (a) Either the diploid
chromosome set of the androgenetic males has arisen from one sole
haploid spermatozoon by means of some kind of diploidization (monospermic, strictly homozygous diploid androgenesis), or (b) the diploid
complex has arisen by means of fusion of two different sperm nuclei
(dispermic, heterozygous diploid androgenesis).
This uncertainty was unquestionably settled by Hasimoto's work
(1934b), where the male parent was homozygous for mutation od and
was at the same time heterozygous for another character semidominant
Kp (supernumerary abdominal legs) and therefore produced 50% odKp
and 50% odkp spermatozoa.
In the first case (monospermic androgenesis), the ratio among exceptional androgenetic od individuals should be according to expectation
1 odod, KpKpil
odod, kpkp, while in the second case of dispermic
androgenesis the expectation is 1 odod, KpKp:2 odod, Kpkpil odod,
kpkp, as in the case of monohybrid F 2 segregation. The results obtained
are unquestionably in favor of dispermic androgenesis and heterozygous
Kpkp males phenotypically different from homozygous KpKp individuals
appeared in the expected quantity. This opens the possibility of producing bipaternal androgenesis, which has been realized by means of double
insemination of a sole female by two different males (Strunnikov, 1958).
A portion of androgenetic individuals inherits in such cases genetical
markers from both fathers, displaying a noticeable hybrid vigor; these
are Έ τ hybrids between two male parents, not forgetting their "third
parent," the "foster mother" that furnishes the androgenetic progeny
with their cytoplasmic organization and supply.
Androgenetic individuals are males without exception, while individuals obtained by means of heat parthenogenesis are always females.
Thus both methods, androgenesis and heat parthenogenesis, when combined might serve as a useful means for sex control in sericulture. Male
cocoons in Bombyx are richer in silk content than those of females, and
deliberate production of pure male offspring is especially desirable.
Unfortunately, the efficiency of heat androgenesis is still very low: (1)
Drastic heating of freshly fertilized eggs in the sensitive (critical) phase
(second prometaphase) which often results in androgenesis induces many
other nuclear and developmental abnormalities lethal for the great majority of embryos; and (2) with respect to the survivors, not all of them
develop along the androgenetic path; a fairly large proportion, in spite
of heat treatment, persist in normal zygotic development by way of
syngamy.