EXTRACHROMOSOMAL ELEMENT DELTA IN<i>DROSOPHILA MELANOGASTER.</i>IV. VARIATION AND PERSISTENCE OF DELTA-ASSOCIATING SECOND CHROMOSOMES IN A NATURAL POPULATION

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[Delta b], symbolized as [δb], is retained by Sb chromosome lines and transmitted through the females to their progeny. Transmission through the males is not directly demonstrable (Minamori 1969a). [delta r], symbolized as [δr], is retained by Sr chromosome lines and transmitted biparentally (Minamori 1971). The multiplication of delta is suppressed at low temperature. All descendant lines derived from Sb-carrying or Sr-carrying flies in which the presence of delta cannot be demonstrated gradually accumulate their specific delta factors over many generations (Minamori 1969b, 1972). The delta factors and the sensitive chromosomes are inseparably associated. This observation led to the assumption that delta may be a copy of a chromosomal gene or a certain agent integrated into the chromosome (Minamori 1972). This assumption was examined in the present study by experiments designed to induce delta-retaining sensitive chromosomes, and to map the gene(s) responsible for delta-retention and/or for sensitivity to the killing action of delta factor. One sensitive chromosome which retained [δb] (Sb chromosome) was obtained in the presence of [δb] out of 2492 insensitive chromosomes which retained no delta; in addition one Sb chromosome was obtained in the presence of [δr] out of 2131 insensitives. The latter finding suggests that Sb might be induced by a mutation caused by [δb] or [δr], but not by integration of either delta into the chromosome. Four Sb chromosomes and one sensitive chromosome which retained [δr] (Sr chromosome) were obtained out of 1970 insensitives when males carrying the chromosome were fed an alkylating mutagen, ethyl methane sulfonate (EMS). The location of delta-retaining genes was examined by crossing-over experiments employing eight Sb and five Sr chromosomes. The genes on these chromosomes were found to be located in the same region or near one another. The gene for [δb], symbolized as Dab, and the gene for [δr], symbolized as Dar, are assumed to be multiple alleles of a locus at 2-24.9. The sensitivity of the chromosomes was modified appreciably by recombination; hence, the genes controlling this trait are assumed to be a polygenic system. The findings obtained in this study lead to the hypothesis that delta may be produced by a chromosomal gene (Da) and transmitted extrachromosomally.

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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EXTRACHROMOSOMAL ELEMENT DELTA IN DROSOPHILA MELANOGASTER. IX. INDUCTION OF DELTA-RETAINING CHROMOSOME LINES BY MUTATION AND GENE MAPPING

Minamori

Sugimoto

1973

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“…Recently, mutator factors or male recombination factors have been discovered several natural populations: In Pennsylvania (present experiment), J ! londa (VOELKER 1974), North Carolina (CARDELLINO andMUKAI 1975), Texas (HIRAZUMI 1971;SLATKO and HIRAZUMI 1973), and Japan (MINAMORI et al 1970, although they later pointed it out as a mutator; MINAMORI and ITO 1971).…”

Section: Discussionmentioning

confidence: 99%

VARIATION OF SPONTANEOUS OCCURRENCE RATES OF CHROMOSOMAL ABERRATIONS IN THE SECOND CHROMOSOMES OF DROSOPHILA MELANOGASTER

Yamaguchi

Mukai

1974

After accumulating mutations by the aid of marked inversions, spontaneous occurrence rates of chromosome aberrations were estimated for 1148 chromosome lines that originated from five stem line second chromosomes of Drosophila melanogaster. In chromosome lines originating from three stem chromosomes (CH, PQ, and RT), mutations were accumulated for 7550, 7252, and 7256 chromosome generations, respectively, but no structural change was detected. For the chromosome lines that originated from the other two stem chromosomes, the situation was different: Twenty aberrations (19 paracentric inversions and 1 translocation between the second and the third chromosomes) during 45990 chromosome generations took place in the 500 chromosome lines derived from stem line chromosome (AW), and 92 aberrations (83 paracentric inversions, 6 pericentric inversions, 2 translocations between the second and the third chromosomes and 1 transposition) arose during 45006 chromosome generations in the 500 chromosome lines derived from stem line chromosome (JH). For the AW group the occurrence rate becomes 0.00043 per chromosome per generation for all aberrations and 0.00041 for inversions. For the JH group the corresponding rates are 0.00204 and 0.00198, respectively.—A non-random distribution of the breakpoint on the salivary gland chromosome was observed and the breakpoints were concentrated in the regions 26, 29, 33, and 34.—The cytoplasms and the chromosomes (other than the second chromosomes) were made approximately uniform throughout the experiments. Thus, this remarkable variability in the occurrence rate is most probably due to the differences in one or more chromosomal elements on the original five stem chromosomes. The mutable chromosomes (AW and JH) appear to carry a kind of mutator factor such as hi (Ives 1950).

EXTRACHROMOSOMAL ELEMENT DELTA IN DROSOPHILA MELANOGASTER. VII. RELATION TO FERTILITY IN A SECOND-CHROMOSOME LINE

Minamori¹,

Ito

1972

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The IDb-45 chromosome line usually carries an appreciable amount of delta b, but it is not susceptible to the killing action of this delta. The fertility of this line was examined when it carried various amounts of delta b. More than one third of the Cy/IDb-45 males and females tested became sterile when they carried cytoplasm of the Cy/Pm stock which is assumed to carry no delta b. The number of progeny is smaller when flies of this line are raised at 25°C than at 28°C at which temperature the multiplication of delta is accelerated. The progeny number was appreciably reduced when the flies were raised at 18°C at which temperature the multiplication of delta is suppressed. This line could not be maintained at that temperature, since both males and females became sterile. Thus, the conclusion may be drawn that the presence of an appreciable amount of delta b is necessary for the gametogenesis of the Cy/IDb-45 flies.