An Analysis of Male-Recombination Elements in a Natural Population of DROSOPHILA MELANOGASTER in South Texas

Gonadal dysgenesis determinants in a natural population of Drosophila melanogaster

Three populations of Drosophila melanogaster from northern California were surveyed for the ability to produce and resist gonadal dysgenesis in the P-M system of hybrid dysgenesis. Males from all three populations produced low to moderate levels of gonadal dysgenesis in crosses to Oregon-R M females. Most females had the P cytotype, but the M cytotype occurred occasionally. The three populations could not be statistically differentiated from one another, but were easily distinguished from populations from Australia and Wisconsin on the basis of gonadal dysgenesis potential. The California populations had higher levels of M cytotype than did the Wisconsin population. Thirteen X chromosomes and 11 pairs of autosomes were extracted from one of the California populations, using a modification of the standard balancer chromosome technique to suppress hybrid dysgenesis during extraction. All lines produced strongly skewed sterility distributions in crosses to M-strain females, and mean levels of sterility were less than 50%. There was evidence of nonadditive interactions between the autosomes. Most extraction lines had the P cytotype, but M and intermediate cytotypes were observed. Some of the intermediate cytotypes were stable over time. Lines were tested at two different times after extraction. Some lines evolved higher sterility potential as they were kept in the laboratory, even in the presence of P cytotype. The results point out a number of deficiencies in current genetic and population genetic models of hybrid dysgenesis and imply that gonadal dysgenesis is unlikely to be an important evolutionary force in this population.

Genetic instability in Drosophila melanogaster: the genetics of an MR element that makes complete P insertion mutations

An MR element that maps to a specific locus in chromosome 3 of Drosophila melanogaster has the unusual feature of producing complete P (a mobile element) sequence mutations at several X chromosome loci. This MR also increases the frequency of mitotic recombination. Evidence is given for the transposition of MR. The complete P insertion mutations are autonomously unstable and are capable of causing otherwise stable incomplete (defective) P insertion mutations to revert. These results complement the analysis of P element functions with a synthetic complete P derivative. The genetic basis for the mutational-mitotic recombinational components of "hybrid dysgenesis" is conveniently explicable in terms of MR elements present in the genomes of flies present in the wild.

An SD (segregation distribution)-MR (male recombination) chromosome isolated from a natural population of Drosophila melanogaster

A second chromosome line ofDrosophila melanogaster(S-90), isolated from a northern California natural population, is able to induce (1) an increased frequency of X-chromosome visible mutations, (2) male recombination activity subject to reciprocal cross suppression, and (3) strong meiotic drive from heterozygous males. Based upon several lines of evidence (including the response to suppressor chromosomes of both systems) we conclude thatS-90contains bothSD(Segregation Distortion) andMR(PorI) chromosome activity. The two systems appear to behave independently and simultaneously, and a small centromeric region of theS-90chromosome appears to contain the major genetic elements of both systems.

Cytotype polymorphism of the P-M system in two wild populations of Drosophila melanogaster

In Drosophila melanogaster the interactions of the P-M system generate germ-line aberrations (e.g., sterility, mutations) found in certain interstrain hybrids. Two wild populations, from France and Tunisia, were examined in order to determine the distribution of the chromosomal P factor and the extrachromosomal cytotypes. No P factors active for potential GD sterility were found in these populations. But search for the M cytotype, which causes susceptibility to the P factors, and for the P cytotype, which causes resistance to the P factors, showed that both populations are polymorphic for the cytotypes. Such a polymorphism seems to be stable in the wild, at least over a 2-year period. Mutator activity (measured by generated mutations at the sn and ras loci) was found to be present. Some possible interactions between cytotype polymorphism, mutator activity, and the structure of Drosophila populations are discussed.

Similarity of centromeric heterochromatin in strains of drosophila melanogaster which interact to produce hybrid dysgenesis

Many long-established laboratory strains of D. melanogaster interact with recently-collected wild-type strains, so that the progeny show sterility, enhanced mutation, male recombination and other degenerative traits, a syndrome known collectively as "hybrid dysgenesis". Tests have been made for differences in centromeric heterochromatin between interacting strains, by comparing homologues in mitotic preparations from hybrid individuals. Differences between homologues have not been revealed, either qualitatively by C-banding or quantitatively by in situ hybridisation to RNA transcripts from satellites 1.705 and 1.686. However, the sensitivities of the techniques are such that quantitative differences of less than 50% between strains could escape detection.

A model of the negative correlation between male recombination and transmission frequency in Drosophila melanogaster

A model is proposed to account for the phenomenon of negative correlation between male recombination (theta) and transmission frequency (kappa) in Drosophila melanogaster. The model assumes that, in some stage or stages of development, the male recombination elements cause a particular event that does not occur in normal males and that this event, in turn, induces with certain probabilities male recombination and/or sperm dysfunction. The regression equations of theta on kappa predicted by the model were compared with those actually observed. There was generally excellent agreement between them.

Parameters of Male and Female Recombination Influenced by the T-007 Second Chromosome in DROSOPHILA MELANOGASTER

The T-007 second chromosome line of Drosophila melanogaster, previously shown to contain genetic elements responsible for male recombination induction, appears to affect several parameters of recombination in females. In T-007 heterozygous females, the distribution of recombination (but not the total frequency) is changed from that observed in control females; relative increases are observed in the more proximal regions of the second, third and X chromosomes, while relative decreases are observed more distally. These changes are paralleled by altered coefficient of coincidence values and in an increased nondisjunction frequency of second chromosomes. The distribution of recombination in females is strikingly similar to that observed in males as measured along the second and third chromosomes, and the frequency of nondisjunction of the X and Y chromosomes is increased in T-007 heterozygous males. Based upon these results and responses to the effect of structurally rearranged heterologues (the "interchromosomal effect"), it is suggested that T-007 affects the preconditions for meiotic exchange in females. It is not yet known if elements responsible for these effects are the same elements responsible for the numerous other traits associated with the T-007 second chromosome.