RESUMO
Mariner-like elements (MLE) are members from class II of transposable elements also known as DNA transposons. These elements have a wide distribution among different groups of organisms, including insects, which can be explained by horizontal and vertical gene-transfer. MLE families have been described in tephritid flies and other genera. During screening for Wolbachia bacteria in fruit flies of the genus Anastrepha, we discovered two sequences related to mariner-like elements. Based on these sequences, we designed primers that allowed us to isolate and characterize two new mariner-like elements (Anmar1 and Anmar2) in Anastrepha flies. These elements, which belong to the mellifera and rosa subfamilies have a low nucleotide diversity, and are probably inactive and acquired by vertical transfer. This is the first report of mariner-like transposons in flies found in South America.
Assuntos
Proteínas de Ligação a DNA/genética , Tephritidae/classificação , Tephritidae/genética , Transposases/genética , Animais , FilogeniaRESUMO
Dosage compensation refers to the process whereby females and males with different doses of sex chromosomes have similar amounts of products from sex chromosome-linked genes. We analyzed the process of dosage compensation in Sciara ocellaris, Diptera of the suborder Nematocera. By autoradiography and measurements of X-linked rRNA in females (XX) and males (XO), we found that the rate of transcription of the single X chromosome in males is similar to that of the two X chromosomes in females. This, together with the bloated appearance of the X chromosome in males, support the idea that in sciarids dosage compensation is accomplished by hypertranscription of the X chromosome in males.
Assuntos
Dípteros/genética , Mecanismo Genético de Compensação de Dose , Transcrição Gênica , Cromossomo X , Animais , DNA , Feminino , MasculinoRESUMO
Sciara ocellaris (Bradysia tritici) is a dipteran species characterized by an extensive polymorphism of structural modifications of single bands occurring in the polytene chromosomes. In this experiment we obtained estimates of egg-to-adult viabilities in relation to the genotypes determined by 15 different loci. In spite of the presence of considerable levels of linkage disequilibrium possibly generated by random sampling genetic drift, it is suggested that at least one out of 15 polymorphic modified chromomeric loci is maintained in the population by an overdominance mechanism.
Assuntos
Dípteros/genética , Polimorfismo Genético , Animais , Bandeamento Cromossômico , Cruzamentos Genéticos , Feminino , Genótipo , Masculino , Modelos Genéticos , Glândulas Salivares/ultraestrutura , Estatística como AssuntoRESUMO
O presente trabalho descreve 19 faixas heterozigotas (ou assimétricas) que ocorrem nos cromossomos politênicos de Sciara ocellaris, sendo 11 no cromossomo A, três no cromossomo B, quatro no cromossomo C e uma no cromossomo X. A assimetria das faixas pode ser agrupada em três classes: (1) uma faixa grossa; (2) uma faixa fina oposta à duas faixas grossas e (3) uma faixa grossa em um cromossomo sem que haja correspondente no cromossomo homólogo. O polimorfismo para as faixas é muito extenso. Na presente amostra, as 368 larvas, provenientes de uma populaçäo mantida em caixa no laboratório, eram heterozigotas, em média, para 4,95 ñ 0,10 das 15 faixas analisadas. Estudo da assimetria das faixas de larvas em estágios que antecedem e que säo posteriores à amplificaçäo do DNA na glândula salivar, mostrou que a assimetria näo é devida à amplificaçäo diferencial de DNA em cromômeros homólogos. A origem dessas aberraçöes ainda é uma incognita. Deficiências parciais ou duplicaçöes devem, portanto, ser as causas de sua formaçäo
Assuntos
Animais , Bandeamento Cromossômico , Cromossomos/citologia , DNA , Heterozigoto , Insetos , Polimorfismo Genético , Glândulas SalivaresRESUMO
The pattern anomaly double abdomen was induced in embryos of Bradysia tritici (syn. Sciara ocellaris) by irradiation of the anterior egg pole with far UV (254 or 285 nm) using low UV fluences. The maximum yield of 18% of double abdomens was obtained when 2.5 h embryos were irradiated (late intravitelline cleavage stage); earlier irradiation failed to yield double abdomens, as did irradiations after the early syncytial blastoderm stage. Exposing irradiated embryos to photoreverting light (366 nm) reduced the yield of malformations. Most double abdomens were symmetrical and the number of segments ranged from 3 to 8 in each set, with the mean value at 6.4 segments.
RESUMO
It was previously assumed that the X-linked recessive mutation, sepia, induced errors in X-chromosome elimination during early embryogenesis of Sciara ocellaris. The results obtained in the present analysis corroborate this assumption and permit a further classification of the type of error this mutation induces. Among 85,244 individuals analyzed, three kinds of aberrant flies were identified: mosaics (0.01%), gynandromorphs (0.42%) and phenotypically exceptional individuals (0.25%). The origin of these abnormal flies could be ascribed to errors in selective elimination of X chromosomes that occur in male meiosis or during the early cleavages of the zygote nuclei. This last kind of error could be classified into three types: (a) error in number, (b) error in type, and (c) error in number and type of X chromosome eliminated. Evidence is provided indicating that sepia has no direct effect on the X chromosome; it has a maternal influence and exerts its effect only in the heterozygous condition.