Nota prévia sôbre a meiose de Corizus (Liorhyssus) hyalinus (Fabr.) (Hemiptera-Corizidae)
| Autor: | S. de Toledo Piza Jor. |
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| Rok vydání: | 1946 |
| Předmět: | |
| Zdroj: | Anais da Escola Superior de Agricultura Luiz de Queiroz, Volume: 3, Pages: 141-148, Published: 1946 Anais da Escola Superior de Agricultura Luiz de Queiroz; v. 3 (1946); 141-148 Anais da Escola Superior de Agricultura Luiz de Queiroz Escola Superior de Agricultura Luiz de Queiroz (ESALQ-USP) instacron:USP |
| ISSN: | 0071-1276 2316-8935 |
| DOI: | 10.1590/s0071-12761946000100008 |
| Popis: | The main facts presented in this paper may be summarized as follows: 1) Corizus (Liorhyssus) hyalinus (Fabr.) has primary spermatocytes provided with 6 autosomal tetrads, one pair of microchromosomes and one sex chromosome. 2) The two microchromosomes present in this species sometimes appear at the primary metaphase as an unequal pair of minute elements. In the secondary spermatocytes the unique microchromosome present may be in the limit of visibility or entirely invisible. This invisibility may be partly due to a loss of colourability. 3) The sex chromosome divides transversely in the first division of the spermatocyte, passing undivided to one pole in the second one. In the latter it becomes fusiform in the beginning of anaphase revealing in this manner its dicentricity. In late anaphase it finishes by passing to one pole leaving in the other pole one of its kinetochores sometimes accompanied by a chromosomal fragment. 4) All the chromosomes divide transversely in both divisions, a diagram being enclosed to elucidate the question. 5) Spermatogonial chromosomes are provided with one kinetochore at each end, being curved toward the poles since the most beginning anaphase. 6) The following hypothesis is presented as an essay to explain the origin of microchromosomes: Since microchromosomes parallel sex chromosomes in most respects, as for instances in heteropycnosis and pairing modus, it seems highly probable that they originate from sex chromosomes. One may suppose that the ancestral form of a given species had a sex chromosome which used to lose a small centric fragment when it divided during meiosis. This fragment might well be at first an unstable one. Later, to compensate the effects of such a deficiency a mechanism arose through evolution which produced two useful results : a) the establishment of the fragment as a permanent structure of the cell nucleus and b) the acquirement by the sex chromosome of the faculty of passing to one pole without losing any of its ends. |
| Databáze: | OpenAIRE |
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