Soldadura por uma das extremidades de dois cromossômios homólogos do tityus

Piza Jor., S. de Toledo

doi:10.1590/S0071-12761946000100019

Resumo

In this paper the author describes a very interesting case of union of two homologous chromosomes of the scorpion Tityus bahiensis just by the opposite extremities. The two normal pairs of chromosomes behave as ordinarily, the members of each pair showing at times a slight disturbance in their regular parallelism. The complex chromosome, on the contrary, behaves itself as if it were devoid of kinetochores, that is, it does not orient like normal chromosomes nor reveal any kind of active movement. The fusion of the chromosomes has resulted from terminal breakage at the opposite ends, the correspondig fragments having been found unpaired in a cell in which two pairs of chromosomes were present. Consequently, the compound chromosome, like the normal ones, is provided with a kinetochore at each one of the free ends. Being thus a centric chromosome its behavior, or more exactly, its kinetic inactivity may be compared with that of the monovalents found elsewhere in meioses. It is due o the failure of a partner. The fusion of two homologous chromosomes has transformed them into a new chromosomal unit in whose corresponding parts the ability of pairing was entirely abolished. This result is in full contradiction with the theory of a point-to point attraction between homologous chromosomes attributed to particular power of the genes, since, if genes really exist, being placed in their original loci, they would promote the union side by side of the members of the compound chromosome. If an attraction loci-to-loci should prevail the compound chromosome would be bent as in Fig. 8, C or form a ring similar to the loops observed in the inverted segment of sailvary chromosomes of Drosophila, as represented in the Fig. 8, D and this, in accordance with the order of the loci resulting from an union of corresponding or opposite ends of the fused chromosomes, as indicated in the Fig, 8 A and B. The evidence in hand points to a fusion by non homologous extremities. The expected rings, however, have never been found in metaphase plates. From this fact the author concludes that there is no point-to-point attraction between chromosomes, a conclusion in full agreement with the behavior of Hemipteran chromosomes which, in spite of geing composed of two equivalent halves do not bend in order to adjust the corresponding loci. (Cf. the papers on Hemiptera published by the author in this volume).

Soldadura por uma das extremidades de dois cromossômios homólogos do tityus

S. de Toledo Piza Jor.

Professor de Zoologia, Anatomia e Fisiologia da Escola Superior de Agricultura "Luiz de Queiroz" - Universidade de São Paulo

SUMMARY

In this paper the author describes a very interesting case of union of two homologous chromosomes of the scorpion Tityus bahiensis just by the opposite extremities. The two normal pairs of chromosomes behave as ordinarily, the members of each pair showing at times a slight disturbance in their regular parallelism. The complex chromosome, on the contrary, behaves itself as if it were devoid of kinetochores, that is, it does not orient like normal chromosomes nor reveal any kind of active movement. The fusion of the chromosomes has resulted from terminal breakage at the opposite ends, the correspondig fragments having been found unpaired in a cell in which two pairs of chromosomes were present. Consequently, the compound chromosome, like the normal ones, is provided with a kinetochore at each one of the free ends. Being thus a centric chromosome its behavior, or more exactly, its kinetic inactivity may be compared with that of the monovalents found elsewhere in meioses. It is due o the failure of a partner. The fusion of two homologous chromosomes has transformed them into a new chromosomal unit in whose corresponding parts the ability of pairing was entirely abolished. This result is in full contradiction with the theory of a point-to point attraction between homologous chromosomes attributed to particular power of the genes, since, if genes really exist, being placed in their original loci, they would promote the union side by side of the members of the compound chromosome. If an attraction loci-to-loci should prevail the compound chromosome would be bent as in Fig. 8, C or form a ring similar to the loops observed in the inverted segment of sailvary chromosomes of Drosophila, as represented in the Fig. 8, D and this, in accordance with the order of the loci resulting from an union of corresponding or opposite ends of the fused chromosomes, as indicated in the Fig, 8 A and B. The evidence in hand points to a fusion by non homologous extremities. The expected rings, however, have never been found in metaphase plates. From this fact the author concludes that there is no point-to-point attraction between chromosomes, a conclusion in full agreement with the behavior of Hemipteran chromosomes which, in spite of geing composed of two equivalent halves do not bend in order to adjust the corresponding loci. (Cf. the papers on Hemiptera published by the author in this volume).

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LITERATURA CITADA

BLEIER, H. 1931 - Zur Kausalanalyse der Kernteilung. Genetica, 13 :27-76.
BLEIER, H. 1933 - Die meiose von Haplodiplonte. Genetica, 15: 129-136.
PIZA, S. de Toledo, Jor. 1942 - Dorso-ventralidade dos cromossômios. Rev. de Agr. 17: 154-168.
PIZA, S. de Toledo, Jor. 1943 - Meiosis in the male of the brasilian scorpion Tityus bahiensis. Rev. de Agr. 18: 248-276.
PIZA, S. de Toledo, Jor. 1943a - A propósito da meiose do Tityus bahiensis Rev. de Agr. 18: 351-369.
PIZA, S. de Toledo, Jor. 1944 - A case of spontaneous end-to end permanent union of two non homologous chromosomes in the brasilian scorpion Tityus bahiensis accompanied by irregularities in pairing. Rev. de Agr. 19 : 133-147.
PIZA, S. de Toledo, Jor. 1945 - Comportamento do heterocromossômio em alguns Ortópteros do Brasil. An. Esc. Sup. Agr. Luiz de Queiroz", 2 :173-207.