Outcrossing in the homothallic oomycete,Pythium ultimum,detected with molecular markers

The oomycete Pythium ultimum is homothallic, thus a single isolate completes the sexual stage in pure culture. It has been generally assumed that homothallic oomycetes are predominantly inbreeding. In P. ultimum, antheridia occasionally develop from hyphae not directly connected to the oogonium and appear to participate in fertilization, suggesting a possible mechanism for outcrossing. We have used molecular markers to confirm that outcrossing can occur between isolates of P. ultimum. Genetic markers based on randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphisms (RFLP) were used to distinguish isolates in a collection of P. ultimum. Two isolates displaying a high level of polymorphism were mixed and placed on media which allows the development of the sexual stage. RAPD markers were used to screen single oospore progeny to identify potential hybrids between the two parental isolates. Subsequent self-fertilization of one putative F₁ yielded a F₂ population which demonstrated segregation and independent assortment of RAPD and RFLP markers. A similar strategy was used to show that an isolate which is incapable of producing oospores in pure culture can outcross when mixed with a homothallic isolate. These results suggest that other homothallic oomycetes may be capable of outcrossing, and sexual reproduction may, therefore, play an important role in the generation of variation in homothallic oomycetes.     

Genomic and phenotypic evaluation of Salmonella typhimurium and Salmonella enteritidis in Iran

Genomic and phenotypic evaluation of Salmonella typhimurium and Salmonella enteritidis by two simple, fast, and applicable methods of random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) and antibiotic susceptibility for employment in epidemiologic surveillance screening systems in Iran was the objective in this study. We selected 60 (30 S. typhimurium and 30 S. enteritidis) isolates from different animal sources and different times and places among 1975–2006 in Iran. Serotyping with traditional method and reliable antisera was done and then confirmed with multiplex PCR (with four and three pair of primers, respectively). All of S. typhimurium and S. enteritidis isolates have virulence genes of invA and spv, respectively. Then, from nine primers, two primers that have enough discriminatory power were selected for RAPD analysis. We set up the quality and quantity of DNA template, primers, MgCl₂, Taq DNA polymerase, and deoxyribonucleotide triphosphates concentration for RAPD analysis. We also examined the strains with disk diffusion standard antibiotic susceptibility test. With the application of primer P1254; we saw four and seven and primer 23L, six and three profiles in RAPD analysis and 13 and six profiles of R-type in susceptibility test of S. typhimurium and S. enteritidis, respectively. Combination of two methods differentiated these 30 strains to 20 and 16 different profiles, respectively. The finding of this study indicated that clonality of S. enteritidis is more than S. typhimurium in Iran and RAPD-PCR in combination with antibiotic susceptibility test were fast, easy, relatively reliable, and discriminatory molecular and phenotypic methods in the differentiation of S. typhimurium and S. enteritidis for epidemiologic purposes in Iran.     

Mitochondrial genome sequences and comparative genomics of <Emphasis Type="Italic">Phytophthora ramorum</Emphasis> and <Emphasis Type="Italic">P. sojae</Emphasis>

The sequences of the mitochondrial genomes of the oomycetes Phytophthora ramorum and P. sojae were determined during the course of complete nuclear genome sequencing (Tyler et al., Science, 313:1261,2006). Both mitochondrial genomes are circular mapping, with sizes of 39,314 bp for P. ramorum and 42,977 bp for P. sojae. Each contains a total of 37 recognizable protein-encoding genes, 26 or 25 tRNAs (P. ramorum and P. sojae, respectively) specifying 19 amino acids, six more open reading frames (ORFs) that are conserved, presumably due to functional constraint, across Phytophthora species (P. sojae, P. ramorum, and P. infestans), six ORFs that are unique for P. sojae and one that is unique for P. ramorum. Non-coding regions comprise about 11.5 and 18.4% of the genomes of P. ramorum and P. sojae, respectively. Relative to P. sojae, there is an inverted repeat of 1,150 bp in P. ramorum that includes an unassigned unique ORF, a tRNA gene, and adjacent non-coding sequences, but otherwise the gene order in both species is identical. Comparisons of these genomes with published sequences of the P. infestans mitochondrial genome reveals a number of similarities, but the gene order in P. infestans differed in two adjacent locations due to inversions and specific regions of the genomes exhibited greater divergence than others. For example, the breakpoints for the inversions observed in P. infestans corresponded to regions of high sequence divergence in comparisons between P. ramorum and P. sojae and the location of a hypervariable microsatellite sequence (eight repeats of 24 bp) in the P. sojae genome corresponds to a site of major length variation in P. infestans. Although the overwhelming majority of each genome is conserved (81–92%), there are a number of genes that evolve more rapidly than others. Some of these rapidly evolving genes appear specific to Phytophthora, arose recently, and future evaluation of their function and the effects of their loss could prove fruitful for understanding the phylogeny of these devastating plant pathogens. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Three copies of the ATP2 gene are arranged in tandem on chromosome X in the yeast Saccharomyces cerevisiae

We previously reported that there were three copies of ATP1 coding for F₁- and two copies of ATP3 coding for F₁- on the left and right arm of chromosome II, respectively. In this study, we present evidence that there are three closely linked copies of ATP2 encoding the subunit of the F₁F₀-ATPase complex on the right arm of chromosome X in several laboratory strains, including Saccharomyces cerevisiae strain S288C, although it was reported by the yeast genome project that ATP2 is a single-copy gene. Chromosome X fragmentation, long-PCR, chromosome-walking and ATP2-disruption analysis using haploid wild-type strains and prime clone 70645 showed that the three copies of ATP2 are present on the right arm of chromosome X, like those of ATP1 on chromosome II. Each was estimated to be approximately 4 kb apart. We designated the ATP2 proximal to the centromere as ATP2a, the middle one as ATP2b and the distal one as ATP2c. The region containing the three ATP2s is composed of two repeated units of approximately 7 kb; that is, both ends (ATP2a, ATP2c) accompanying the ATP2-neighboring ORFs are the same. A part of YJR119c, YJR120w, YJR122w (CAF17) and YJR123w (RP55), which were reported by the yeast genome project, are contained in the ATP2 repeated units; and the middle ATP2 of the three ATP2s, ATP2b, is located between the two repeated units. Expression of all three copies of ATP2 (ATP2a, ATP2b, ATP2c) was confirmed because a single or double ATP2-disruptant could grow on glycerol, but a triple ATP2-disruptant could not. In addition, of the three copies of ATP1 and ATP2, even if only one copy of the ATP1 and ATP2 genes remained, the cells grew on glycerol.     

Genome differentiation by GISH in interspecific and intergeneric hybrids of tomato and related nightshades

We employed genomic in situ hybridization to analyze the chromosomal constitution and pairing of interspecific and intergeneric hybrids involving cultivated tomato (Lycopersicon esculentum) and two related wild nightshade species, Solanum lycopersicoides and S. sitiens. Using standard stringency conditions, the tomato genome was readily distinguished from that of the two nightshades, whereas the latter were only distinguishable under increased stringency. These observations indicate a more distant phylogenetic relationship between L. esculentum and the Solanum group, and suggest S. lycopersicoides and S. sitiens share a high degree of sequence homology. Chromosomal associations during meiosis of interspecific and intergeneric hybrids were consistent with these relationships: chromosomes of F₁ L. esculentum×S. lycopersicoides and F₁ L. esculentum×S. sitiens hybrids frequently formed univalents during diakinesis. In contrast, F₁ S. lycopersicoides×S. sitiens hybrids showed complete bivalent formation. L. esculentum×S. sitiens hybrids, including the F₁ plants, a monosomic addition, and an allotetraploid, showed lower frequencies of pairing between homeologous chromosomes than the corresponding L. esculentum×S. lycopersicoides genotypes. A trigenomic 2n+14 hybrid, with 12 extra chromosomes from S. sitiens and 2 from S. lycopers icoides, displayed mostly homologous chromosome associations. The distribution of rDNA genes appeared similar in the three genomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of a molecular genetic linkage map for <Emphasis Type="Italic">Colletotrichum lindemuthianum</Emphasis> and segregation analysis of two avirulence genes

A framework genetic map was developed for the fungal pathogen Colletotrichum lindemuthianum, the causal agent of anthracnose of common bean (Phaseolus vulgaris L.). This is the first genetic map for any species within the family Melanconiaceae and the genus Colletotrichum and provides the first estimate of genome length for C. lindemuthianum. The map was generated using 106 haploid F1 progeny derived from crossing two Mexican C. lindemuthianum isolates differing in two avirulence genes (AvrclMex and AvrclTO). The map comprises 165 AFLP markers covering 1,897 cM with an average spacing of 11.49 cM. The markers are distributed over 19 major linkage groups containing between 5 and 25 markers each and the genome length was estimated to be approximately 3,241 cM. The avirulence genes AvrclMex and AvrclTO segregate in a 1:1 ratio supporting the gene for gene hypothesis for the incompatible reaction between C. lindemuthianum and P. vulgaris, but could not be incorporated into the genetic map. This initial outline map forms the basis for the development of a more detailed C. lindemuthianum linkage map, which would include other types of molecular markers and allow the location of genes previously isolated and characterized in this species.     

Genetic analysis of intergeneric hybrids obtained by protoplast fusion in yeasts

Summary Prototrophic hybrids have been obtained by the fusion of various auxotrophic haploid strains of Saccharomyces cerepisiae and Schwanniomyces castellii. The fusion hybrids showed starch fermentability which derived from one of the fusion parents, S. castellii. Surprisingly, these fusion hybrids were found to exhibit excellent sporulation and spore germination. The progenies of these fusion hybrids showed a few aberrant segregations, but mostly normal segregation for auxotrophic genetic markers. They also showed many tetrads with an apparently digenic segregation (2:2, 3:1 and 4:0) for starch fermentation. On the other hand, mating types of segregants of the fusion hybrids were determined by the prototrophic recovery method. Consequently, tetrad types for mating type were mostly 2a:1:1 non-mater and several asci showed tetrad types of 2a:2 non-mater and 2a:2. The 60 prototrophic fusion hybrids and its segregants did not secrete -amylase on the starch agar plate. However, all of the data suggested that fusion hybrid could carry two dominant genes (STAB and STAC) to ferment starch, and that the two genes STAB and STA2 may be identical or allelic as may be the genes STAC and STA3.     

Tn5 mutagenesis of the Salmonella typhimurium 100 kb plasmid: definition of new virulence regions

In this study, the 100 kb plasmid of Salmonella typhimurium, which is known to contribute to the pathogenicity of the organism, was tagged with the transposon Tn5 to define regions of the plasmid contributing to overall virulence. Eleven randomly selected vir::Tn5 plasmids carried by the plasmid-free S. typhimurium strain WS1321 were physically mapped and then examined in mice for subcutaneous LD₅₀ value, ability to induce splenomegaly, and ability to grow to high numbers in the spleens of infected mice. Nine strains were found to be virulence-attenuated and showed varied levels of growth in the spleens of subcutaneously infected BALB/c mice. Eight of these nine strains carried Tn5 insertions which lie outside the previously defined virulence region. These studies corroborate the findings of other investigators as well as defining novel regions of the 100 kb virulence plasmid involved in the pathogenicity of this organism.     

Single-locus control of sucrose octaacetate tasting among mice

SWR/J mice avoid sucrose octaacetate (SOA) solutions at concentrations which other inbred strains do not. This phenotypic difference has been hypothesized to result from variation at a single autosomal locus with two alleles, one dominant (Soa ^a , aversion) and one recessive (Soa ^a , blind). Data from reciprocal F₁ and F₂ crosses of SWR/J (taster) and C57BL/6J (nontaster) mice and from four generations of selective lineal backcrossing to the C57BL/6J strain, in two-bottle preference tests with 10^–5 M SOA, were used to test this monogenic model against two polygenic models. The phenotypic ratios expected in the segregating generations according to the single-locus model were consistent with the observed ratios. The ratios expected with either two-locus model were inconsistent with those found. A strain distribution pattern, also consistent with monogenic variation, was found when a set of recombinant inbred strains (SWXL/Ty) derived from SWR/J and C57L/J (nontaster) mice was similarly tested. Outbred CFW mice (inbred substrains of which had been reported by separate laboratories to be both SOA tasters and SOA nontasters) were found to be polymorphic for SOA tasting. An allele identical by descent to that in the SWR/J strain may be segregating in this (distantly) related line.This research was supported in part by Grant NS 15560 from the NINCDS.     

Orthogonal field alternation gelelectrophoresis (OFAGE) as a means for the analysis of somatic hybrids obtained by protoplast fusion of different Saccharomyces strains

Summary PEG-induced fusion of two haploid Saccharomyces strains resulted in three morphologically different types of fusion products. In order to estimate the respective ploidy, one representative of each type — F ₁, F ₂ and F ₃ — was subjected to a measurement of the cellular DNA content and to a meiotic segregation analysis. The data obtained in these analyses suggested the strain F ₁ to be a haploid cybrid resulting from mere plasmogamy, whereas the hybrids F ₂ and F ₃ were likely to be the products of a successful nuclear fusion of two, respectively three, protoplasts of the parental strains. However, the complete genetic composition of the hybrids could only be revealed by OFAGE experiments, as the genetic data solely referred to a few chromosomes with marker genes. All the results of the OFAGE were in full accordance with the assumptions made in the conventional analysis, thus indicating the OFAGE to become a very promising means for the investigation of hybrids inaccessible to genetic analyses.     

Cytoplasmic inclusion cistron of Soybean mosaic virus serves as a virulence determinant on Rsv3-genotype soybean and a symptom determinant

Soybean mosaic virus (SMV; Potyvirus, Potyviridae) is one of the most widespread viruses of soybean globally. Three dominant resistance genes (Rsv1, Rsv3 and Rsv4) differentially confer resistance against SMV. Rsv1 confers extreme resistance and the resistance mechanism of Rsv4 is associated with late susceptibility. Here, we show that Rsv3 restricts the accumulation of SMV strain G7 to the inoculated leaves, whereas, SMV-N, an isolate of SMV strain G2, establishes systemic infection. This observation suggests that the resistance mechanism of Rsv3 differs phenotypically from those of Rsv1 and Rsv4. To identify virulence determinant(s) of SMV on an Rsv3-genotype soybean, chimeras were constructed by exchanging fragments between avirulent SMV-G7 and the virulent SMV-N. Analyses of the chimeras showed that both the N- and C-terminal regions of the cytoplasmic inclusion (CI) cistron are required for Rsv3-mediated resistance. Interestingly, the N-terminal region of CI is also involved in severe symptom induction in soybean.     

Introgression of Lilium Rubellum Baker Chromosomes into L. Longiflorum Thunb.: A Genome Painting Study of the F1 Hybrid, BC1 and BC2 Progenies

Interspecific hybrids between Lilium longiflorum (L, 2n=2x=24) andLilium rubellum (R, 2n=2x=24) were produced with the aim of transferring desirable horticultural traits from L. rubellum to L. longiflorum. All F₁ hybrids (LR, 2n=2x=24) and BC₁ individuals (LLR, 2n=3x=36) were phenotypically uniform for plant height, flowering time, leaf shape and flower colour. The BC₁ plants were, in spite of their triploid nature, fertile and could be used as a female parent in backcrossings with autotetraploid L. longiflorum (LLLL, 2n=4x=48). Twelve BC₂ individuals were obtained and three of them were selected for further chromosome analysis. As L. longiflorum and L. rubellum chromosomes were indistinguishable in the hybrids, genomic in- situ hybridization (GISH) was applied to establish the parentage of the chromosomes of the F₁ hybrids and the BC₁ and BC₂ progenies. GISH confirmed the LLRR constitution of the doubled amphimonoploid (allodiploid), and the LLR constitution of all BC₁ plants. The three selected BC₂ plants were, as expected, aneuploid, containing three complete sets of L. longiflorum chromosomes and six, seven or eight L. rubellum chromosomes, respectively. However, L/R translocation or recombinant chromosomes could not be demonstrated in the mitotic metaphase complements of the F₁, BC₁ and BC₂ plants. In spite of the high frequencies of homoeologous recombination in the F₁ hybrids (LR) pollen was found to be sterile in all cases. At metaphase I of the pollen mother cells of the BC₁ plants, genome painting did not reveal any cases of homoeologous pairing and recombination between L and R chromosomes. This lack of exchange between homoeologous chromosome segments indicates complete preferential pairing of the L and R chromosomes in the F₁ (amphidiploid) and BC₁ plants. It seems that the preferential pairing in the F₁ and BC₁ hybrids hinder the introgression of the chromosome segments or species-specific genes into the recipient for breeding purposes.     

Virulence of an exotoxin A-deficient strain of Pseudomonas aeruginosa toward the silkworm, Bombyx mori

We studied the contribution of exotoxin A to the virulence of Pseudomonas aeruginosa against the silkworm, Bombyx mori. First, an exotoxin A-deficient mutant strain (PAO1toxA) was created, and its virulence compared with that of the parental PAO1 strain. In a short-term mortality assay, the mutant harboring pBBR1MCS2 did not kill B. mori until 120 h after inoculation and complementation of the corresponding gene in trans restored the strain’s virulence. Next, to ascertain whether or not it lost all virulence, PAO1toxA (pBBR1MCS2, pGFP) was used in a long-term mortality assay. B. mori inoculated with the mutant strain did not die until early in the 5th instar (240 h after inoculation). However, 50% of the inoculated B. mori died late in the 5th instar or in the early pupal stage (408 h after inoculation). All had died by the pupal stage (600 h after inoculation). The mutant strain was isolated from dead larvae and cocoons. The bacterial population of PAO1toxA in hemolymph reached 4.77 × 10⁷ cfu/ml. These results indicated that exotoxin A acts as a virulence factor in B. mori and that other virulence factor(s) are involved during the late stages of infection.     

Nucleotide sequences and characterization of haemolysin genes from Aeromonas hydrophila and Aeromonas sobria

Extracellular haemolysin is thought to be one of the important virulence factors in Aeromonas infection. Two extracellular haemolysin genes (AHH3 and AHH4) from Aeromonas hydrophila strain 28SA, one (AHH5) from A. hydrophila strain AH-1 and one (ASA1) from Aeromonas sobria strain 33 were cloned into cosmid and plasmid vector DNA in Escherichia coli. The nucleotide sequences of the open reading frames of AHH3 and AHH4 are both 1476 basepairs (bp), whereas AHH5 and ASA1 are 1455 and 1467 bp in length, respectively. The deduced amino acid sequences of AHH3, AHH4, AHH5 and the previously reported aerolysin from A. hydrophila showed a significant degree of sequence homology of over 90% each. The amino acid identity of the ASA1 haemolysin and those from A. hydrophila and Aeromonas trota aerolysins ranged from 58–68%. From DNA hybridization analysis using our cloned haemolysin genes as probes, we found that the AHH5 and ASA1 DNA probes hybridized with about 31 and 75% strains of motile Aeromonas species, respectively. The activity of haemolysins of cloned genes were different in medium agar containing various erythrocytes.     

Oral administration of a dominant T-cell determinant peptide inhibits allergen-specific TH1 and TH2 cell responses in Cry j 2–primed mice

Background: Oral immunotherapy with a peptide for allergic immune responses is theoretically a promising therapy but has not been established yet. Objective: To evaluate immune suppressive efficacy of oral administration of an immunodominant peptide, we investigated changes in T-cell proliferation, T_H1 - and T_H2 -cytokine production, and T_H1 - and T_H2 -mediated antibody production in mice after oral administration of a peptide. Methods: Peptide p246-259, containing a dominant T-cell determinant of Cry j 2, which is the major allergen in Japanese cedar pollen, was used in this study. Groups of mice received p246-259 or PBS alone before or after they were primed intranasally with Cry j 2 and cholera toxin. In another experiment mice were primed intraperitoneally with Cry j 2 and alum. Proliferative response and cytokine production by nasal-associated lymph node cells against Cry j 2 were investigated. Amounts of systemic anti-Cry j 2 IgE and IgG antibodies were also measured. Results: Oral administration of the peptide to mice before, or even after, the sensitization induced oral tolerance in T-cell responses against the allergen; the tolerance was associated with decreased production of T_H1 (IFN-γ and IL-2) and T_H2 (IL-4) cytokines. Allergen-specific T_H1 -mediated (IgG2a and IgG2b) and T_H2 -mediated (IgG1 and IgE) antibody responses were also inhibited. Conclusions: Oral administration of a dominant T-cell determinant peptide induces immunologic tolerance in both T_H1 and T_H2 cell responses against the whole protein allergen. Our study is the first, to our knowledge, to demonstrate the potential for peptide-based oral immunotherapy in order to treat allergic immune responses. (J Allergy Clin Immunol 1998;102:961-7.)     

Age dependence of skin autofluorescence

The nontryptophane intrinsic fluorescence of finger pad skin was studied in men aged 20–70 years in order to evaluate the possibility of using this parameter as a biomarker of aging. Linear correlation coefficients (r) between the fluorescence intensity and age varied from 0.50 to 0.66 for various skin sites. Age dependence of the mean value of fluorescence (F) measured on 4 fingers can be approximated by a second-degree polynomial:F=2.82−0.083T+0.0014T ² (r ₁=0.64,r ₂=0.71), whereT is chronological age in years. The proposed measurement of skin autofluorescence is a simple, noninvasive, rapid test for evaluating the aging of the skin in subjects over 40 with a high age-related determination (r ²=0.5). Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 3, pp. 351–353, March, 1999     

An evaluation of the inactive mouse X chromosome in somatic cell hybrids

The expression of mouseZfx, Rps4, Ube1x, andXist was evaluated in hamstermouse somatic cell hybrids containing either an active or an inactive mouse X chromosome using polymerase chain reaction of reverse transcribed RNA (RT-PCR). The results showed thatZfx, Rps4, andUbe1x are expressed exclusively from the active mouse X, whileXist is expressed exclusively from the inactive X. These findings confirm the pattern of X inactivation for these mouse genes reported previously based on expression in somatic tissues of F₁ females from interspecific crosses. These results demonstrate the existence of differences between human and mouse X inactivation, as the corresponding human genes,ZFX, RPS4X, andUBE1 escape X inactivation.     

Cloning of serotonin 5-HT1 receptor subtypes from the chimpanzee, gorilla and Rhesus monkey and their agonist-induced guanosine 5′γS triphosphate binding

5-HT₁ receptor subtypes (_1B, _1D and _1F) have been implicated in migraine pathophysiology and their ligands have been examined for pharmacological actions in various experimental animal models. Considerable divergences exist, however, in their primary sequences between experimental animals and human, and additional models closer to human, such as non-human primates seem to be useful for migraine research. Earlier, we cloned the 5-HT_1D, and here 5-HT_1B and 5-HT_1F receptors from the chimpanzee, gorilla and Rhesus monkey, via polymerase chain reactions with their genomic DNAs and primers designed from the corresponding human receptors. Direct sequencing of PCR products showed that the 5-HT_1B receptors from the chimpanzee, gorilla and monkey differ from the human receptor by 0, 1 and 7 residues, respectively while 5-HT_1F receptors differ by 0, 3 and 10 residues, respectively. These divergent residues are mostly conservatively substituted and also largely confined to the N-terminal region and the 3rd intracellular loop, away from transmembrane segments and intracellular loops near membrane which are critical for ligand binding and G protein coupling. The chimpanzee 5-HT_1D, 5-HT_1B and monkey 5-HT_1F receptors, as heterologously expressed in human embryonic kidney 293 cells, showed robust agonist-induced guanosine 5′gamma ³⁵S triphosphate (GTPγ³⁵S) binding through activation of G proteins containing Gγ_i subunits. Moreover, pronounced inhibition of basal GTPγ³⁵S binding by methiothepin (an antagonist), representing constitutively active receptors, was observed with only 5-HT_1D. Overall, ligand binding and GTPγ³⁵S binding profiles for these primate receptors are comparable to those for the human receptors and validate non-human primates as useful models for human migraine research.     

Selection for high and low mating propensity inDrosophila ananassae

InDrosophila ananassae, artificial selection was carried out for high and low mating propensity for 15 generations. Response to selection was from about F₅, with rapid divergence in mating frequencies in replicates of both fast and slow lines. To assess the effect of selection on the two sexes, females and males of the selected lines were tested against their respective counterparts of the control line after 15 generations. Significant differences in mating propensity were observed when selected males were tested against the control females, which suggests that males were much more affected by selection than females. After 15 generations the fast and slow lines (both replicates) were crossedinter se and mating frequencies of F₁ hybrids were studied in the same way as during the selection experiment. F₁ flies had a higher mating activity compared to their parental lines when males were derived from fast lines to produce hybrids. On the other hand, F₁ hybrids produced by crossing slow-line males with fast-line females showed mating frequencies similar to those of the slow parental lines. These findings suggest that mating propensity inD. ananassae is under the control of polygenes. Furthermore, the significant differences in mating propensity of hybrids produced by the fast and slow males indicate the possibility of a Y-linked influence on mating propensity inD. ananassae.The present investigation was carried out during the tenure of a senior research fellowship of the CSIR, New delhi, to S.C.