Heteromorphisms of Ag stained nucleolus organizer region [NORs] in acrocentric chromosomes of Egyptians

The nucleolar organizer region [NORs] of the acrocentric chromosomes of 80 normal Egyptians [40 males, 40 females] were studied using the Ag-staining technique [NSG]. The Ag-staining of NORs varied from one individual to the other, yet a consistent pattern of Ag +ve NORs was present in each individual. The modal number of Ag +ve NORs per cell ranged from 6 to 10. The average modal number of Ag +ve NORs per individual was 7.65. No sex difference was observed in the sample studied. The size distribution of silver +ve NORs revealed that very large NORs occurred with a frequency of 7%. The frequency of large NORs was 24.13%, medium sized NORs was 30.75%, small sized NORs was 14.62%, while the frequency of absent NORs was 23.5%. A racial difference in the expression as well as in the size of NORs is proposed. Only one individual [1.25%] was identified as possessing a double NORs [dNORs]

Spatial distribution of homologous chromosomes in metaphase plates of human lymphocytes

The frequency of homologous chromosome association/pairing of chromosomes 1 to 22 and X was analysed in 1000 metaphase plates with colcemid and in 500 plates without colcemid from normal human lymphocyte cells. Statistical analysis revealed that the occurrence of somatic homologous association/pairing is non-random. Chromosomes 1,3,7,16,19 and 20 were found to be associated more frequently The occurrence and significance of such association/pairing is most probably related to the structural and functional organisation of chromosomes. The phenomenon of homologous chromosome pairing is discussed as one of the possible aetiological factors for aneuploidy and/or uniparental disomy

Frequency of satellite association in infertile patients

Investigations were carried out on general pattern and frequency of acrocentric association in a group of patients suffering from infertility [azoospermia and oligospermia]. Two types of parameter, absolute association frequency and relative association frequency, were used. A significantly higher frequency of satellite association was found in the fourty eight hour cultured lymphocytes of oligospermic patients for either type of association parameter in comparison with that of both azoospcrmics and healthy persons. Apart from only one azoospermic patient, no significant difference was found between azoospermics and healthy persons for both absolute and relative association frequency. It is proposed that satellite association may predispose the D-group chromosome to translocate with each other and suggest that this may be a primary cause of oligospermia

The asymmetric bands of the polytene chromosomes of Sciara ocellaris (Diptera; sciaridae)

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

Cytogenetic study of Trichechus inunguis (Amazonian Manatee)

A constituiçäo cromossômica do peixe-boi da Amazônia, Trichechus inunguis (Mammalia, Trichechidae), foi estudada em cinco animais machos e quatro fêmeas oriundos da bacia Amazônica, através da coloraçäo convencional de Giemsa e bandamentos G-, C-e RON. O número diplóide da espécie é 2n = 56 com NF = 82. A heterocromatina constitutiva está presente na regiäo centromérica de todos os cromossomos e os genes organizadores de nucléolos estäo localizados na constriçäo secundária do braço curto do par 20, sendo observado heteromorfismo na coloraçäo-RON entre os homólogos. A análise comparativa entre o cariótipo de T. inunguis e de T. manatus determinado por White et al. (1976) sugere que rearranjos cromossômicos do tipo Robertsoniano podem ter sido responsáveis pelas diferenças cariotípicas entre essas duas espécies