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PubMed1990

Genetics of inbred Drosophila melanogaster. XXIII. Diversity in cytoplasmic elements affecting recombination.

From an inbred line of Drosophila melanogaster, in which both marker genes in the X-chromosome and an autosomal inversion had been induced, we introduced the genome into cytoplasms of various sources. Two or eight sister-lines were established from three sets of cytoplasms. Tests of recombination in the distal y--rb region in isogenic females revealed similarity in early broods within sets of sister-lines, but differences between different sources of cytoplasms. Later broods showed increasing recombination and also greater variability. There was a clear excess of recombination in offspring to inversion-heterozygous females. In the set with eight sister-lines there were two groups of four, which during the first 4.5 years had been propagated with 14 and 28 days generation interval respectively. These two groups differed in the inter-chromosomal effect in early broods. The possibility is discussed that there are more than one set of extra-chromosomal elements that affect recombination in the distal region of the X-chromosome. It is concluded that selective forces operate on the extra-chromosomal elements in other ways than in the process with which they were traced in the tests. The consequences of diversities in extra-chromosomal elements are discussed.

Animals↗
PubMed1990

Genetics of inbred Drosophila melanogaster. XXV. Simultaneous tests of I-inductivity and M-type.

From a branch of an inbred line of Drosophila melanogaster we introduced the genome into cytoplasms from various sources. Among a pair of sister-lines, which at first showed R-type in the I-R system, one line switched to I-type. From a branch of this I-type line, for several generations kept at 18 degrees C, we established sub-lines derived from four single females. They were propagated at 25 degrees C with 14 or 28-day generation interval, respectively. It was presumed that 14-day generation interval gave strong, and 28 days interval gave weak R-elements. Tests of the strength of the I-inductivity disclosed no relation to the assumed strength of the R-elements. By the same test technique, primary non-disjunction and chromosome loss, the M-type was studied in the eight sub-lines. There appeared diversities in the M-type, assumed to be related to chromosomal mutations. Both primary non-disjunction and chromosome loss were affected by the P-M reaction.

Animals↗
PubMed1989

Genetics of inbred Drosophila melanogaster. XXI. Re-reversion in the strength of R-elements.

In tests of the I-R hybrid dysgenesis system in Drosophila melanogaster we have in former tests examined the transition from strong to weak R-type by modifying the breeding protocol as regards the generation length, achieved by collecting parental flies from early or late egg-laying. To examine if independent occurrence of weak R-elements showed similar or different response at re-reversion of the generation interval, four sublines were tested. It was found that transition from long to short generation interval eventually resulted in a stepwise change to strong R-type. The change towards strong R-type occurred at a slightly slower rate than we earlier found in the opposite direction at transfer towards weak R-type. From lines bred at 14 days generation interval at 25 degrees C we kept, as a safeguard, branches at 18 degrees C. After 27 generations, tests of the strength of the R-reactivity revealed that various cytoplasms showed a depressed R-reactivity with no heterogeneity between sister lines. Return of sub-branches from 18 degrees to 25 degrees C for a couple of short generations (14 days) or a single long generation (28 days) showed results indicating heteroplasmy for weak and strong R-type elements in the branches kept at 18 degrees C. The vulnerability of the R-elements is a useful model for tests of extrachromosomal heredity, which may shed light on the problems involved in identifying other extrachromosomal systems.

Animals↗
PubMedDate not supplied

Variants of Mta, the mouse maternally transmitted antigen, determined by three alleles of the extrachromosomal gene Mtf.

Two new forms of Mta, the maternally transmitted antigen of the mouse, were defined by cytotoxic T lymphocytes. One is found in laboratory mice carrying the beta allele of the maternally transmitted factor, Mtf, which were previously thought to be Mta-negative. The other is associated with a new allele, Mtf gamma, and is found in wild mice from Toulouse. Like the common form of Mta, determined by the extrachromosomal Mtf alpha, the new forms are also dependent on the a allele of Hmt, a chromosomal gene linked to H-2, and are associated with beta 2-microglobulin. Killers could be raised in all six combinations of alpha, beta, and gamma mice, showing that each form of Mtf determines a distinct (set of) epitope(s). We propose that the product of the Hmt gene, a class I MHC antigen, presents a peptide derived from a mitochondrial gene product on the cell surface and thereby creates the target antigen, Mta.

Alleles↗
PubMed1975

Molecular vehicle properties of the broad host range plasmid RK2.

The pladmid RK2 is stably maintained in a broad range of gram-negative bacteria. The RK2 DNA has a single Eco RI restriction site. The insertion of a DNA fragment into this site does not interfere with either plasmid maintenance or self-transmissibility. Because RK2 has a broad host range, it should be useful for the construction in vitro of hybrid plasmid molecules capable of being established by conjugal transfer or transformation into many genera of gram-negative organisms.

Conjugation, Genetic↗