An analysis of white-mottled mutants inDrosophila hydei,with observations on X-Y exchanges in the male

Chromosomes and phenotypes of four different sex-linkedwhite-mottled mutants of the position-effect variogation type were studied. Three mutants (w ^m1,w ^m2,w ^m3) are X-chromosomal rearrangements which shift the w⁺ locus into a position close to heterochromatin, but which have different ouchromatic and heterochromatic breaks. The fourth, a spontaneous derivative ofw ^m1, is an insertional duplication of part of the X chromosome, including thew ⁺ andN ⁺loci. The duplicated segment is inserted into the distal part of the long arm of the heterochromatic Y chromosome. It is designated,w ^m CoY, orXw ^m Co when transferred to the X chromosome.Three chromosomal types (w ^m1,w ^m CoY) and (Xw ^m Co) having the same cuchromatic break near thew ⁺ locus, cause large-spotted eyes whereas two others (w ^m2,w ^m3) produce a popper-and-salt type of mottling. From the position of the various eu- and heterochromatic breaks, it appears that the distance of thew ⁺ locus to the point of reunion with heterochromatin, rather than the amount or type of adjoining heterochromatin, dietates the phenotypic action of the displacedw ⁺ locus, in the sense of a spreading effect on two proposed functional subunits within thew ⁺ locus.The pigmentation background against which the mottling effect is produced, i.e., a givenw-allele with its characteristic colour, or other eye colour mutations, does not seem to affect the type of mottling. Drosopterins and ommochromes react in the same way to modifing factors like temperature and supernumerary Y chromosomes. Two mutants (w ^m2 andw ^m CoY) while reacting in the same manner to Y chromosomes showed an opposite temperature response.By exchange between the heterochromatin of the Y and X chromosome inw/w ^m CoY males thew ^m Co duplication was transferred between the sex chromosomes with a certain regularity. It is not yet known wether the exchanges are mitotic or meiotic in origin but their heterochromatic nature has been demonstrated cytologically.     

X-Y exchanges in males of Drosophila hydei carrying the w m Co duplication

Males carrying, inserted on their Y chromosome, a small fragment of X including the w ⁺ (and N ⁺) locus (white-mottled Confluens, w ^m Co), were crossed with the purpose of scoring exceptional progeny. Some of the male and female exceptions were progeny tested and further analysed. Among the various mechanisms which may lead to exceptional offspring, X-Y exchanges proved to occur with a not negligible frequency. The rate was 3%. Nondisjunction accounts for the bulk of the remaining exceptions and appears to be increased considerably in the presence of rearrangements on one or the other of the sex chromosomes.The w ^m Co fragment after having been switched from Y to X by some mechanism other than regular crossing over, may become retransferred to a normal Y chromosome, but at a rate below 3%.     

A marked ring-Y-chromosome in Drosophila hydei with a new type of white variegation

A ring-Y chromosome, R(Y)w ^m, of D. hydei is described which carries a complete set of fertility genes, a NOR region and a small X-chromosomal insertion (w ^m), which may be used as a marker. The ring has been characterized by various staining techniques. It was derived from a w ^mCo Y chromosome by X-ray treatment of spermatocytes. Its mode of origin allows to fix the gene order in the distal region of the long arm of the w ^mCoY chromosome. The white ⁺ gene included in the ring shows a new type of position-effect variegation which is described and discussed in the context of an earlier hypothesis on a dual function of the white locus.     

Y chromosome-specific mutations induced by a giant transposon in Drosophila hydei

Summary The w ^m Co duplication of Drosophila hydei (Dp (1; Y) 16B2-17B1) contains 13–16 bands in salivary gland chromosomes. The duplication resides preferentially in the X heterochromatin or on the Y chromosome. In some stocks frequent (up to 4×10^-3) exchanges of the duplication occur between different Y chromosomes (T(X; Y) and free Y) or between the X and the Y chromosome. About 60% of the T(X; Y)-Y exchanges induce mutations in the Y chromosomal male fertility genes of the recipient Y chromosome. From the mutational spectrum generated by the T(X; Y)-Y transpositions and from the variable efficiency as acceptor of different X-Y translocations it can be concluded that the exchanges show a remarkable site specificity: distal positions in the long arm of the Y chromosome are occupied preferentially. More proximal positions in the long arm of insertions into the short arm of the Y chromosome are found only with a lower frequency. No transpositions to the autosomes have been recovered. Duplications are lost with highly differing frequencies. The losses are not linked with insertions of the w ^m Co element into a new position and are more frequent than transpositions. Therefore, we regard the w ^m Co element as a giant transposon.     

Characterization of Parasarcophaga heterochromatin

The heterochromatin of neuroblast metaphase chromosomes in six sympatric species of Parasarcophaga was characterized by C-, N-, quinacrine (Q)-, Hoechst 33258 (H)-, Hoechst/actinomycin D (H/AMD)- and acridine orange (AO)-banding. The autosomes and the sex chromosomes in all the six species are characterized by the presence of C- and N-positive heterochromatin. The N-bands lie within the limits of the C⁺ heterochromatin. AT-specific fluorochromes further differentiate heterochromatin into Q⁺H⁺,Q^–H⁺ and Q^–H^– types and the repetitive nature of these regions is indicated by their fast reassociating nature with AO-staining. Thus, on the basis of these results, the heterochromatin of mitotic chromosomes in Parasarcophaga can be classified into C⁺N⁺Q⁺H⁺, C⁺N⁺Q^–H^–, c⁺n^–q^–h^– and C^–N^–Q^–H⁺ types.     

The genetic analysis of a large transposing element of Drosophila melanogaster

A member of Ising's family of large transposing elements (TEs) has inserted into, or very near, the crinkled (ck, 2–50) locus. This TE (TE36) carries functional alleles of both the white and roughest loci, and causes a hypomorphic mutation of ck. The TE is visible in polytene chromosomes as a two-banded insertion between 35B9 and 35C1. These bands show homology to foldback (FB) elements by in situ hybridization. All spontaneous losses of TE36 remain mutant for ck and retain sequences homologous to FB at the site of TE's insertion. TE36 carries only one functional copy of w ⁺, by the criterion that z w, TE36/ + flies are wild-type for eye color but z w; TE36/TE36 flies are zeste. This white⁺ gene is dosage compensated since w/Y; TE36/+ males have twice as much eye pigment as w/w; TE36/ + females. A form of the TE that has four polytene chromosome bands and expresses twice as much pigment as TE36 has been recovered. However, its white genes are not suppressed by zeste.     

The NOTCH Locus of DROSOPHILA HYDEI: Alleles, Phenotypes and Functional Organization

The Notch (N) locus of Drosophila hydei and a series of its alleles and phenotypes are described. Some models are discussed to explain the opposite effects of some alleles on the structure of the wing, the neomorphic action of N^Ax over typical N alleles and the interaction with the mutation Costal-nick (Cnk).     

Nurse cell polytene chromosomes of Drosophila melanogaster otu mutants: Morphological changes accompanying interallelic complementation and position effect variegation

Combinations of certain mutant alleles of the ovarian tumor gene permit the production of viable eggs. Two alleles that behave in this way are otu⁷ and otu¹. Females homozygous for either allele are sterile, and their ovarian nurse cells (NC) contain giant polytene chromosomes of various morphologies. Fertile flies (otu⁺ / otu⁺, otu⁻ / otu⁷, otu⁺ / otu¹¹) have endopolyploid nurse cells with typical dispersed chromosomes. Fertile hybrids (otu⁷ / otu¹¹) produce large numbers of polytene chromosomes comparable to, and often larger than, classic salivary gland (SG) chromosomes. Therefore, these otu hybrids provide a unique system for studying, at the chromosomal level, the activation and expression of genes functioning during oogenesis. The otu gene encodes a long and a short isoform. The normal long isoform appears to be responsible for the dispersion of chromosomes during the endomitotic DNA replications occurring in ovarian NCs. The genetic inactivation of euchromatic genes placed next to pericentric heterochromatin by a chromosomal rearrangement is accompanied by the compaction of corresponding chromosome regions. A comparative study of the manifestation of position-effect variegation for the polytene chromosomes of SG cells and NCs was made using the Dp(1;1)pn2b and Dp(1;f)1337 rearrangements. The percentage frequencies of block formation in the SG and NC nuclei for Dp (1;1) pn2b rearrangement were 92.6% vs. 15.8%, respectively; for Dp(1;f) 1337, these values were 56.8% vs. 9.7%. Therefore heterochromatin belonging to germ line chromosomes is in a configuration that is far less likely to inactivate inserted segments of euchromatin than is heterachromatin from somatic chromosomes. Dev. Genet. 20:163–174. 1997. © 1997 Wiley-Liss, Inc.     

Relationships within the Melanogaster subgroup species of the genus Drosophila (Sophophora)

Five members of the melanogaster species subgroup of the subgenus Sophophora have been studied cytologically, their mitotic chromosomes analysed after Giemsa, C-banding and quinacrine staining. In all five species (D. yakuba, D. teissieri, D. erecta, D. orena and D. mauritiana) n=4 and all of the species except D. orena have a typical melanogaster like mitotic karyotype though there are clear differences between species in the distribution of both C⁺ and Q⁺ material. D. orena has large metacentric X and Y chromosomes due to the accumulation of intensively fluorescing material on these elements with respect to their homologues in melanogaster. This extra heterochromatin of D. orena correlates with a very high proportion of satellite DNA in its nuclear genome (S. Barnes, unpublished). The polytene chromosomes of these species were studied after quinacrine staining and Q⁺ material found to be restricted to the polytene fourth chromosomes, with the exception of D. orena which possesses considerable Q⁺ material in its chromocentre. These findings are discussed in the light of other studies of karyotype evolution in the genus Drosophila.     

Genetic instability in Drosophila melanogaster: Transpositions of the white gene and their role in the phenotypic expression of the zeste gene

Summary Seven independent transpositions of the w ⁺ gene have been recovered as derivatives of two separate direct tandem duplications of the white locus. The transpositions map to discrete sites on both major autosomes. Five transpositions were employed to study the role of w ⁺ gene dos-age on zeste (z) gene expression. Each transposition generates a unique zeste phenotype; one transposition is not predictive for another. A functional allele of zeste, z ^77h, responds to w ⁺ gene dosage contrary to the z response.Supported by NIH grant GM22221     

A mutable white-inversion in Drosophila melanogaster

Summary From a zeste mutant stock with a mutable white locus a new mutant (z w ^w ) was isolated. It has a white-eyed phenotype and a short X-chromosome inversion (In(1)w ^w ) which extends from salivary chromosome bands 3B2-C1 to 4B4-C1. In giant chromosomes of heterozygotes the inversion is unusually tightly paired. Probably because of this intimate pairing the recombination frequencies for regions near the inversion are not decreased in comparison to those for structurally normal chromosomes. The inversion chromosome is mutable. The mutations which arise have pigmented eyes and can be subdivided into two groups. One group is characterized by a re-inversion to normal chromosome structure. The mutability of the white locus appears to be independent of the inversion and reinversion. The process of reinversion is discussed.     

Influence of salinity on Na+ and K+ accumulation, and gas exchange in Avicennia germinans

We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψ_w) and leaf osmotic potential (Ψ_s) decreased. Leaf Ψ_w was at least −0.32 MPa lower than the Ψ_w of solution. Na⁺ and K⁺ ions explained about 78 % of decrease in Ψ_s. K⁺ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely, Na⁺ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P _N) and stomatal conductance (g _s) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO₂ concentration (C _i) followed the same trend. The P _N as a function of C _i showed that both the initial linear slope and upper plateau of the P _N vs. C _i curve were markedly affected by high salinity (40 and 55 ‰).     

The recombinational analysis of aberrations and the position of the notch locus on the polytene chromosome of Drosophila

Summary The recombinational analysis of heterozygotes for a point-mutant N and a deficiency N suggests that the map region approximated by the interval fa to nd ² is at the right edge of salivary band 3C7 or in the interband to the right. The map region N ^55ell to fa can be anywhere between the left interband and the right edge of 3C7. We discovered that small inversions also can be used in the recombinational analysis, and the inversion data support the conclusions already described.The reactivation of latent mutability in a Notch inversion resulted in reinversion of the original aberration, followed by reversion of N to N ⁺. From the same Notch inversion, we isolated a spontaneous deficiency superimposed upon the original aberration, which supported our hypothesis that two of our w to N deficiencies probably originated as deficiencies superimposed upon inversions.     

An Increase in the X-Linked Lethal Mutation Rate Associated with an Unstable Locus in DROSOPHILA MELANOGASTER

The behavior of an unstable allele of the singed-bristle locus on the X chromosome was studied in connection with the occurrence of lethal mutations on that same chromosome. The unstable allele, weak singed (sn^w), is under the control of the P-M system of hybrid dysgenesis and, in the M cytotype, mutates secondarily to extreme singed (sn^e) and to wild type (sn⁺) at high rates. Chromosomes whose sn^w allele had mutated in this fashion sustained lethal mutations at a rate of 3%; whereas, those whose sn^w allele had apparently remained unchanged, acquired lethals at a lower rate, 1.3%. The significant difference between these values indicates a statistical coincidence between the phenomena of sn^w instability and X-linked lethal mutation induction. This coincidence can be explained by postulating that mutations at the singed locus sometimes release a genetic element capable of reinserting elsewhere in the chromosome. Alternately, sn^w instability and lethal induction might be associated because they are the effects of a common cause, perhaps some mutation-inducing substance present in various amounts in the germ cells of dysgenic flies.—The lethals that occurred on chromosomes whose sn^w allele had mutated to sn^e mapped preferentially close to singed. The lethals on the sn^w and sn⁺ chromosomes did not show this concentration on the map. Cytological analysis of samples of all three types of lethal chromosomes indicated that, with one exception, there was no detectable breakage at the singed locus itself. The single instance of breakage at singed was not associated with any change in the singed phenotype. Thus, the instability of sn^w apparently does not involve detectable breakage of the singed locus, or if it does, this breakage is not a common event.     

Chromosomal structure is altered by mutations that suppress or enhance position effect variegation

We examined the genetic, morphological, and molecular effects of position effect variegation inDrosophila, and the effects of mutations that either suppress [Su(var)] or enhance [E(var)] this phenomenon. All eightSu(var) mutations examined strongly suppress the inactivation of variegating alleles of the genes white [In(l) w ^m4 ], brown [In (2R)bw ^VDe2 ] and Stubble [T(2;3)Sb ^V ]. TheE(var) mutation enhances variegation of these loci. The chromosomal region 3C-E (26 bands) which includes the white locus is usually packaged as heterochromatin in salivary glands of the variegating strainw ^m4 . Addition of any of theSu(var) mutations restores a more euchromatic morphology to this region. In situ hybridization to polytene chromosomes and DNA blot analyses of gene copy number demonstrate that the DNA of thew ⁺ gene is less accessible to its probe in the variegatingw ^m4 strain than it is in the wildtype or variegation-suppressed strains. Blot analysis of larval salivary gland DNA indicates that the white gene copy number does not vary among the strains. Hence, the differences in binding of thew ⁺ gene probe in the variegating and variegation-suppressed strains reflect differences in chromosomal packaging rather than alterations in gene number. The effects of variegation and theSu(var) mutations on chromatin structure were analyzed further by DNAse I digestion and DNA blot hybridization. In contrast to their dramatic effects on chromosomal morphology and gene expression, theSu(var) mutations had negligible effects on nuclease sensitivity of the white gene chromatin. We suggest that the changes in gene expression resulting from position effect variegation and the action of theSu(var) mutations involve alterations in chromosomal packaging.     

The genetic basis of resistance and sensitivity to the meiotic drive gene D in the mosquito Aedes aegypti L.

A study has been made on the genetic basis of meiotic drive at the Distorter (D) locus which, in coupling with the male-determining gene (or region) M on the Y chromosome, causes production of excess male progeny. Its effect is regulated by the sensitivity/resistance of the X chromosome. This study demonstrates that there are two major loci controlling resistance/sensitivity to MD: (1) the m gene (or region) on the X chromosome (allelic with M) which may be either m ^R or m ^S (resistant or sensitive), (2) the t (tolerance) gene (or genes) which recombines with m and, if present, largely counteracts the effect of m ^S . There is also evidence that MD itself is capable of limited adaptation.The conclusions were derived from using MD males of the T30 or ACCRA strains (from Trinidad and Ghana respectively). The work involved the use of the CHIPEI and RED strains with sensitive X chromosomes, the latter also carrying the t (tolerance) gene which is linked to re (red eye) and m (the sex-determining locus or region) but recombines with both. The implications of these findings for using MD as a method of population control are discussed.     

Meiosis Aspects and Nucleolar Activity in Triatoma vitticeps (Triatominae, Heteroptera)

Some aspects of both the nucleolar organizer activity and meiosis were studied in the testes of Triatoma vitticeps (Heteroptera, Triatominae). The techniques used included squashing followed by lacto-acetic orcein staining, silver-ion impregnation, fluorescent banding (CMA₃, Quinacrine mustard and DAPI) and fluorescent in situ hybridization (FISH). A close relationship between heterochromatin and nucleolus in testicular cells was observed. During meiosis, the silver-ion impregnation pattern varied. At metaphase plate, a small body appeared apart from the chromosomes. In the spermatids this small body was seen in preparations stained with orcein and silver- ion impregnation but not with fluorochromes or FISH. These characteristics combined suggest that these corpuscles represent a source of ribonucleoproteins (RNP) – RNA and specific nucleolar proteins. Silver-ion impregnation and (FISH) revealed nucleolar organizer activity in two metaphase sex chromosomes (X). These results indicate that, in these species, nucleolar organizer regions (NORs) are located in the sex chromosomes, X chromosomes were CMA₃⁺ and Y chromosome was DAPI⁺.     

A preliminary genetic analysis of TE146, a very large transposing element of Drosophila melanogaster

TE146 is a transposing element (TE) consisting of six polytene chromosome bands that has inserted into the no-ocelli (noc 250) locus. This member of Ising's TE family carries two copies of the white and roughest loci. TE146 is lost from noc with a spontaneous frequency of approximately 1 in 22000 chromosomes. All spontaneous losses are accompanied by the reversion of the noc mutation associated with the TE. The TE is associated with fold-back (FB) sequences. The losses of TE146 retain fold-back homology at noc. Of 26 -ray-induced losses of TE146, 16 are gross deletions, removing loci neighboring noc and ten are not. The non-deleted -ray-induced losses are either noc ^– and rst ⁺ or noc ⁺ and rst ^–. The white⁺ genes of TE146 are dosage compensated since w/Y; TE146/+ and w/w; TE146/+ flies are sexually dimorphic for eye color. These w ⁺ genes are also suppressed by zeste since z w; TE146/+ flies have zeste-colored eyes.     

Genetic instability in Drosophila melanogaster

Summary An unstable long tandem duplication which includes the white locus twice, marked with w ^sp in the left and w ^17G in the right locus, when kept in males has been found to produce red-eyed sons which have lost the long duplication and with it the w ^sp and w ^17G mutants. Such exceptions were produced also when w ^17G had been exchanged for w ^a.Stocks originating from these exceptions are unstable, producing: 1) zeste males, also unstable, 2) w ^- deletions, stable, 3) transpositions of the white locus to sites in other chromosomes.The instability is interpreted as the effect of an IS element, within or adjacent to the white locus, which is supposed to retain a duplication of the proximal zeste interacting part of this locus. According to the orientation of the IS element the duplicated part can be active or inactive, giving a zeste or red eye phenotype.The frequency of exceptional offspring after X-ray treatment of the red and zeste unstable stocks have been compared to stable stocks with corresponding genotypes.