Genetic consequences of linkage between malathion resistance and an autosomal male-determining factor in house fly (Diptera: Muscidae).

The pattern of inheritance of genes conferring resistance to malathion and genetic consequences of linkage between an autosomal male-determining factor and resistance genes on the second chromosome were investigated in a strain of house fly, Musca domestica L., selected for malathion resistance. The second and fifth chromosomes contribute significantly to malathion resistance. The presence of a male-determining factor linked with the resistance genes on the second chromosome resulted in a strong sexual dimorphism in malathion resistance. We also observed that the male-determining factor changed its linkage relationship from the third linkage group to the second linkage group during the selection experiments.     

Sex and death in birds: a model of dosage compensation that predicts lethality of sex chromosome aneuploids

Birds show female heterogamety, with ZZ males and ZW females. It is still not clear whether the W is female-determining, or whether two doses of the Z chromosomes are male-determining, or both. This question could easily be settled by the sexual phenotypes of ZZW and ZO birds, in the same way that the sexual phenotypes of XXY and XO showed that the Y is male determining in humans, but that the dosage of an X-borne gene determines sex in Drosophila. However, despite extensive searches, no ZZW or ZO diploid birds have been satisfactorily documented, so we must assume that these genotypes are embryonic lethals. Given that ZW and ZZ are viable and the W contains few genes it is not clear why this should be so. Here I propose that sex chromosome aneuploids are lethal in chicken because, to achieve dosage compensation, a locus on the W chromosome controls the upregulation of genes on the Z in ZW females. ZO birds would therefore have only half the normal dose of Z-linked gene product and ZZW would have twice the amount, both of which would undoubtedly be incompatible with life. Reports of other aneuploids and triploids are also consistent with this hypothesis.     

Die Speicheldrüsenchromosomen der StechmückeCulex Pipiens L. IV. Der Chromosomale Geschlechtsdimorphismus

In the salivary gland chromosomes of the mosquitoCulex pipiens L. band 10 C 3 of the small chromosome I in female larvae always shows a homozygous heterochromatic balloon, while male larvae are heterozygous for this structure, the homologous band being euchromatic. In males, heterozygous for a male-linked reciprocal translocation, the chromosome with the distinct euchromatic band is always involved in the segmental interchange with an autosome. It is concluded that the euchromatic state of band 10 C 3 represents the male-determining allelomorph, and the heterochromatic state the female-determining allelomorph (M and m, respectively). C. pipiens thus appears to be an excellent example of diplogenotypic determination of sex where the sexes are different in one pair of allelomorphs only. At the chromosomal level, this sexual dimorphism is expressed as a heterochromatic versus an euchromatic state of a single band. The significance of this observation is discussed in connection with the problem of the evolution of sex-determining mechanisms within the Nematocera.     

Identification of the Sex-Determining Region of the Ceratitis Capitata Y Chromosome by Deletion Mapping

In the medfly Ceratitis capitata, the Y chromosome is responsible for determining the male sex. We have mapped the region containing the relevant factor through the analysis of Y-autosome translocations using fluorescence in situ hybridization with two different probes. One probe, the clone pY114, contains repetitive, Y-specific DNA sequences from C. capitata, while the second clone, pDh2-H8, consists of ribosomal DNA sequences from Drosophila hydei. Clone pY114 labeled most of the long arm and pDh2-H8 hybridizes to the short arm and the centromeric region of the long arm. In 12 of the analyzed 19 Y-autosome translocation strains, adjacent-1 segregation products survive to the late pupal or even adult stage and can, therefore, be sexed. This was correlated with the length of the Y fragment still present in these aberrant individuals and allowed us to map the male-determining factor to a region of the long arm representing ~15% of the entire Y chromosome. No additional factors, affecting for example fertility, were detected outside the male-determining region.     

Sex-specific control of growth and differentiation in the Drosophila genital disc, studied using a temperature-sensitive transformer-2 mutation

Mutations of the transformer-2 (tra-2) locus of Drosophila melanogaster cause chromosomally female (XX) animals to develop as males, but have no effect on the development of chromosomally male (XY) animals. In the female genital disc, such mutations cause repression of growth and inhibition of differentiation in the female genital primordium, while allowing growth and differentiation of the otherwise repressed male genital primordium. We used a temperature-sensitive mutation of this locus (tra-2^ts1) to switch development from one sexual pathway to the other. Following development at the male-determining temperature (29°C), subsequent culture of the XX;tra-2^ts1 genital disc in vivo at the female-determining temperature (16°C) allowed the previously repressed female genital primordium to develop and form female genital structures, whereas the formation of male genital elements was grossly disturbed. Conversely, following development at the female-determining temperature, subsequent culture in vivo at the male-determining temperature allowed the formerly repressed male genital primordium to grow and produce male genital structures, and repressed the formation of female elements from the already fully developed female genital primordium. The experiments indicate that the tra-2 product has to operate during the culture period in order to maintain the female state of sex determination, i.e., to promote the development of female structures, as well as to repress that of male structures. The experimental treatments, as well as the results of temperature shifts on developing larvae, resulted in sexual transformation of the anal plates, and clarified the sexual homologies of these structures. In both genitalia and analia, a switch from the female to the male developmental pathway was accomplished more rapidly and effectively than the reverse change.     

Drosophila-Host Genetic Control of Susceptibility to Drosophila C Virus

Interactions between Drosophila C virus (DCV) and its natural host, Drosophila melanogaster, were investigated using 15 geographical population samples infected by intraabdominal inoculation. These strains derived from natural populations of D. melanogaster differed in susceptibility to the DCV(C). One strain was ``partially tolerant'. Isofemale lines obtained from one susceptible and one partially tolerant strain were studied. The partially tolerant phenotype was dominant, and there was no difference between F(1) progeny of direct and reciprocal crosses. Analysis of F(2) progeny showed that neither sex-linked genes nor maternal effects are involved in susceptibility to DCV(C). The partially tolerant strain phenotype was dominant and segregated with chromosome III. Two nonexclusive hypotheses are proposed to explain chromosome III gene action.     

Polymorphism of M factors in populations of the housefly, Musca domestica L., in Turkey

M factors, which determine maleness in Musca domestica, were found on the second, third, fourth and fifth linkage groups in housefly populations of Turkey. As in European populations, the male-determining factor was more frequently located on linkage group III (MIII). Some males homozygous or double heterozygous for M factors were identified. Deviations from a 1:1 sex ratio in favour of males, as well as mosaics for somatic marker mutations and sexual mosaics (gynandromorphs), were also observed. The results reveal an extensive polymorphism in the sex-determining system.     

Two unlinked loci controlling the sex of blue tilapia (Oreochromis aureus)

Sex determination in the blue tilapia (Oreochromis aureus) is thought to be a WZ-ZZ (female heterogametic) system controlled by a major gene. We searched for DNA markers linked to this major gene using the technique of bulked segregant analysis. We identified 11 microsatellite markers on linkage group 3 which were linked to phenotypic sex. The putative W chromosome haplotype correctly predicts the sex of 97% of male and 85% of female individuals. Our results suggest the W locus lies within a few centimorgans of markers GM354, UNH168, GM271 and UNH131. Markers on LG1 also showed a strong association with sex, and indicate the segregation of a male-determining allele in this region. Analysis of epistatic interactions among the loci suggests the action of a dominant male repressor (the W haplotype on LG 3) and a dominant male determiner (the Y haplotype on LG1). These markers have immediate utility for studying the strength of different sex chromosome alleles, and for identifying broodstock carrying copies of the W haplotype.     

Genetic determination of susceptibility to estrogen-induced mammary cancer in the ACI rat: mapping of Emca1 and Emca2 to chromosomes 5 and 18

Hormonal, genetic, and environmental factors play major roles in the complex etiology of breast cancer. When treated continuously with 17beta-estradiol (E2), the ACI rat exhibits a genetically conferred propensity to develop mammary cancer. The susceptibility of the ACI rat to E2-induced mammary cancer appears to segregate as an incompletely dominant trait in crosses to the resistant Copenhagen (COP) strain. In both (ACI x COP)F(2) and (COP x ACI)F(2) populations, we find strong evidence for a major genetic determinant of susceptibility to E2-induced mammary cancer on distal rat chromosome 5. Our data are most consistent with a model in which the ACI allele of this locus, termed Emca1 (estrogen-induced mammary cancer 1), acts in an incompletely dominant manner to increase both tumor incidence and tumor multiplicity as well as to reduce tumor latency in these populations. We also find evidence suggestive of a second locus, Emca2, on chromosome 18 in the (ACI x COP)F(2) population. The ACI allele of Emca2 acts in a dominant manner to increase incidence and decrease latency. Together, Emca1 and Emca2 act independently to modify susceptibility to E2-induced mammary cancer.     

Genetic mapping a meiotic driver that causes sex ratio distortion in the mosquito Aedes aegypti

An endogenous meiotic driver in the dengue and yellow fever vector mosquito Aedes aegypti can cause highly male-biased sex ratio distortion in crosses from suitable genetic backgrounds. We previously selected a strain that carries a strong meiotic drive gene (D) linked with the male-determining allele (M) on chromosome 1 in A. aegypti. Here, we performed segregation analysis of the M(D) locus among backcross (BC(1)) progeny from a driver male and drive-sensitive females. Assessment of sex ratios among BC(2) progeny showed ～5.2% recombination between the M(D) locus and the sex determination locus. Multipoint linkage mapping across this region revealed consistent marker orders and recombination frequencies with the existing reference linkage map and placed the M(D) locus within a 6.5-cm interval defined by the LF159 locus and microsatellite marker 446GAA, which should facilitate future positional cloning efforts.     

Colocalization of a partially dominant gene for yellow seed colour with a major QTL influencing acid detergent fibre (ADF) content in different crosses of oilseed rape (Brassica napus).

Quantitative trait loci (QTLs) contributing to yellow seed colour and acid detergent fibre (ADF) were localized and compared in 3 mapping populations developed from 2 crosses (designated 'YE1' and 'YE2') between 2 distinct sources of true-breeding yellow-seeded oilseed rape (Brassica napus) and 2 different black-seeded genotypes. A clear correlation was observed between seed colour and ADF content in both crosses. In all 3 populations, a major QTL, with a large effect on both seed colour and ADF in multiple environments, was detected at the same position on chromosome N18. In YE1, a second minor QTL, with a small effect on seed colour but not on ADF content, was localized on chromosome N1. In YE2, no QTL was observed on N1; however, 2 minor seed-colour loci were localized to N15 and N5. A second major QTL for ADF was localized in YE1 on N13; in YE2, no other QTLs for ADF were detected. Combined QTL and segregation data for seed colour and ADF content in the different populations suggest that a partially dominant B. napus gene for seed colour on N18 contributes to a reduction in fibre content in different yellow-seeded B. napus genotypes. The other QTLs that were identified appear to represent different genes in the 2 yellow-seeded rapeseed sources, which, in each case, affect only fibre content or seed colour, respectively. Potential candidate genes and implications for marker-assisted breeding of oilseed rape with reduced seed dietary fibre content are discussed.     

The Y chromosome that lost the male-determining function behaves as an X chromosome in the medaka fish, Oryzias latipes

The medaka, Oryzias latipes, has an XX/XY sex-determination system, and a Y-linked DM-domain gene, DMY, is the sex-determining gene in this species. Since DMY appears to have arisen from a duplicated copy of the autosomal DMRT1 gene approximately 10 million years ago, the medaka Y chromosome is considered to be one of the youngest male-determining chromosomes in vertebrates. In the screening process of sex-reversal mutants from wild populations, we found a population that contained a number of XY females. PCR, direct sequencing, and RT-PCR analyses revealed two different null DMY mutations in this population. One mutation caused loss of expression during the sex-determining period, while the other comprised a large deletion in putative functional domains. YY females with the mutant-type DMY genes on their Y chromosomes were fully fertile, indicating that the X and Y chromosomes were functionally the same except for the male-determining function. In addition, we investigated the frequencies of the sex chromosome types in this population over four successive generations. The Y chromosomes bearing the mutant-type DMY genes were detected every year with no significant differences in their frequencies. These results demonstrate that aberrant Y chromosomes behaving as X chromosomes have been maintained in this population.     

The Y-Chromosomal and Autosomal Male-Determining M Factors of Musca Domestica Are Equivalent

In Musca domestica, male sex is determined by a dominant factor, M, located either on the Y, the X or on an autosome. M prevents the activity of the female-determining gene F. In the absence of M, F becomes active and dictates female development. The various M factors may represent translocated copies of an ancestral Y-chromosomal M. Double mutants and germ line chimeras show that M(Y), M(I), M(II), M(III) and M(V) perform equivalent functions. When brought into the female germ line, they predetermine male development of the offspring. This maternal effect is overruled by the dominant female-determining factor F(D). M(I) and M(II) are weak M factors, as demonstrated by the presence of yolk proteins in M(I)/+ males and by the occurrence of some intersexes among the offspring that developed from transplanted M(I)/+ and M(II)/+ pole cells. The arrhenogenic mutation Ag has its focus in the female germ line and its temperature-sensitive period during oogenesis. We propose that M(I) and Ag represent allelic M factors that are affected in their expression. Analysis of mosaic gonads showed that in M. domestica the sex of the germ line is determined by inductive signals from the surrounding soma. We present a model to account for the observed phenomena.     

Epigenetic control of sexual phenotype in a dioecious plant,Melandrium album

Melandrium album (syn.Silene latifolia) is a model dioecious species in which theY chromosome, present only in heterogametic males, plays both a male-determining and a strict female-suppressing role. We showed that treatment with 5-azacytidine (5-azaC) induces a sex change to androhermaphroditism (andromonoecy) in about 21% of male plants, while no apparent phenotypic effect was observed in females. All of these bisexual androhermaphrodites (with the standard male 24,AA +XY karyotype) were mosaics possessing both male and hermaphrodite flowers and, moreover, the hermaphrodite flowers displayed various degrees of gynoecium development and seed setting. Southern hybridization analysis with a repetitive DNA probe showed that the 5-azacytidine-treated plants were significantly hypomethylated in CG doublets, but only to a minor degree in CNG triplets. The bisexual trait was transmitted to two successive generations, but only when androhermaphrodite plants were used as pollen donors. The sex reversal was inherited with incomplete penetrance and varying expressivity. Based on the uniparental inheritance pattern of androhermaphroditism we conclude that it originated either by 5-azaC induced inhibition ofY-linked female-suppressing genes or by a heritable activation of autosomal female-determining/promoting genes which can be reversed, on passage through female meiosis, by a genomic imprinting mechanism. The data presented indicate that female sex suppression inM. album XY males is dependent on methylation of specific DNA sequences and can be heritably modified by hypomethylating drugs.     

Epigenetic control of sexual phenotype in a dioecious plant,Melandrium album

Melandrium album (syn.Silene latifolia) is a model dioecious species in which theY chromosome, present only in heterogametic males, plays both a male-determining and a strict female-suppressing role. We showed that treatment with 5-azacytidine (5-azaC) induces a sex change to androhermaphroditism (andromonoecy) in about 21% of male plants, while no apparent phenotypic effect was observed in females. All of these bisexual androhermaphrodites (with the standard male 24,AA +XY karyotype) were mosaics possessing both male and hermaphrodite flowers and, moreover, the hermaphrodite flowers displayed various degrees of gynoecium development and seed setting. Southern hybridization analysis with a repetitive DNA probe showed that the 5-azacytidine-treated plants were significantly hypomethylated in CG doublets, but only to a minor degree in CNG triplets. The bisexual trait was transmitted to two successive generations, but only when androhermaphrodite plants were used as pollen donors. The sex reversal was inherited with incomplete penetrance and varying expressivity. Based on the uniparental inheritance pattern of androhermaphroditism we conclude that it originated either by 5-azaC induced inhibition ofY-linked female-suppressing genes or by a heritable activation of autosomal female-determining/promoting genes which can be reversed, on passage through female meiosis, by a genomic imprinting mechanism. The data presented indicate that female sex suppression inM. album XY males is dependent on methylation of specific DNA sequences and can be heritably modified by hypomethylating drugs.     

Sex Ratio Distortion Caused by Meiotic Drive in a Mosquito, Culex pipiens L

A genetic factor, distorter (d), has been discovered that upsets the normal sex ratio of 1:1 and results in a large excess of males in Culex pipiens. The effect can be explained by a sex-linked, recessive gene. Males homozygous for the gene (Md/md) produce few female offspring; the effect is not due to postzygotic mortality. During the first meiotic division in spermatogenesis, the shortest chromosome pair, which, according to Jost and Laven (1971), is associated with sex determination, can be seen to be abnormal. In a high proportion of spermatocysts, one of the dyads of the shortest bivalent fragments, and the pieces are distributed irregularly to the daughter cells. It is believed that the female-determining chromosomes fragment. This would give rise to an excess of male-determining sperm. The possible usefulness of this factor for control or for experimental purposes is discussed.     

普通小麦Qz180中一个抗条锈病基因的分子作图(英文)

普通小麦(Triticum aestivum L.)材料Qz180具有良好的抗条锈病特性,经基因推导发现其含有一个优良的抗条锈病的基因,暂定名为YrQz。用Qz180与感病材料铭贤169和WL1分别杂交构建了两个F_2群体,用条中30号条锈菌小种对这两个群体进行的抗性测验表明,YrQz为显性单基因遗传。通过SSR和AFLP结合BSA的方法对这个基因进行了分子作图,结果鉴定出与YrQz连锁的2个SSR标记和2个AFLP标记。根据SSR标记的染色体位置,该基因被定位在2B染色体的长臂上,位于两个SSR位点Xgwm388和Xgwm526之间;两个AFLP标记P35M48(452)和P36M61(163)分别位于该基因的两侧,遗传距离分别为3.4cM和4.1cM。     

水稻核不育系6442S—7显性早熟性的遗传分析

研究了早籼核不育系6442S-7与明恢63等16个中迟熟品种杂交F1及其部分组成F2和B1F1的抽穗期遗传.结果表明,6442S-7具有完全显性早熟特性,主要受2对无连锁关系的显性早熟基因控制.同时,还对IR68,献国、9311和BG1639等其他4个迟熟品种与6442S－7杂交F1和F2代,以及三交F1代的抽穗期进行遗传分析,发现IR68、献国和BG1639等4个迟熟品种均含1对等位的不完全显性抑制基因,可部分抑制6442S－7显性早熟基因的表达。认为6442S－7携带的显性早熟基因对水稻遗传改良具有重要的应用价值。     

Sex Determination in the Fly Megaselia Scalaris, a Model System for Primary Steps of Sex Chromosome Evolution

The fly Megaselia scalaris Loew possesses three homomorphic chromosome pairs; 2 is the sex chromosome pair in two wild-type laboratory stocks of different geographic origin (designated ``original' sex chromosome pair in this paper). The primary male-determining function moves at a very low rate to other chromosomes, thereby creating new Y chromosomes. Random amplified polymorphic DNA markers obtained by polymerase chain reaction with single decamer primers and a few available phenotypic markers were used in testcrosses to localize the sex-determining loci and to define the new sex chromosomes. Four cases are presented in which the primary male-determining function had been transferred from the original Y chromosome to a new locus either on one of the autosomes or on the original X chromosome, presumably by transposition. In these cases, the sex-determining function had moved to a different locus without an obvious cotransfer of other Y chromosome markers. Thus, with Megaselia we are afforded an experimental system to study the otherwise hypothetical primary stages of sex chromosome evolution. An initial molecular differentiation is apparent even in the new sex chromosomes. Molecular differences between the original X and Y chromosomes illustrate a slightly more advanced stage of sex chromosome evolution.     

A new aluminum tolerance gene located on rye chromosome arm 7RS

Rye has one of the most efficient groups of genes for aluminum tolerance (Alt) among cultivated species of Triticeae. This tolerance is controlled by, at least, three independent and dominant loci (Alt1, Alt2, and Alt3) located on chromosome arms 6RS, 3RS, and 4RL, respectively. The segregation of Alt genes and several random amplified polymorphic DNA (RAPD), Secale cereale inter-microsatellite (SCIM), and Secale cereale microsatellite (SCM) markers in three F(2) between a tolerant cultivar (Ailés) and a non-tolerant inbred line (Riodeva) were studied. The segregation ratio obtained for aluminum tolerance in the three F(2) populations analyzed was 3:1 (tolerant:non-tolerant), indicating that tolerance is controlled by one dominant locus. SCIM811(1376) was linked to an Alt gene in the three F(2) populations studied, and three different SCIMs and one RAPD (SCIM811(1376), SCIM812(626), SCIM812(1138), and OPQ4(725)) were linked to the Alt gene in two F(2) populations. This result indicated that the same Alt gene was segregating in the three crosses. SCIM819(1434) and OPQ4(578) linked to the tolerance gene in one F(2) population were located using wheat-rye ditelosomic addition lines on the 7RS chromosome arm. The Alt locus is mapped between SCIM819(1434) and the OPQ4(578) markers. Two microsatellite loci (SCM-40 and SCM-86), previously located on chromosome 7R, were also linked to the Alt gene. Therefore, the Alt gene segregating in these F(2) populations is new and probably could be orthologous to the Alt genes located on wheat chromosome arm 4DL, on barley chromosome arm 4HL, on rye chromosome arm 4RL, and rice chromosome 3. This new Alt gene located on rye chromosome arm 7RS was named Alt4. A map of rye chromosome 7R with the Alt4 gene, 16 SCIM and RAPD, markers and two SCM markers was obtained.