JARA SEGUEL, PEDRO EDUARDO
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Registro de poliploidia en la almeja dulceacuícola Musculium Argentinum (D'ORBIGNY 1835) (SPHAERIIDAE, VENEROIDA)
La poliploidía es un carácter inusual en moluscos bivalvos. Sin embargo, datos citogenéticos documentados para especies de la subfamilia Sphaeriinae (familia Sphaeriidae) del hemisferio norte muestran números cromosómicos que varían desde 36 hasta ca. 247. La almeja dulceacuícola Musculium argentinum (D'Orbigny 1835) presenta un número cromosómico 2n = ca. 130, lo cual muestra que la poliploidía también estaría presente en esféridos sudamericanos. Estos antecedentes citogenéticos sugieren que Sphaeriinae podría constituir un complejo poliploide maduro.
Contenido de ADN nuclear en Galaxias Platei (Steindachner, 1898) (Teleostei: Osmeriformes: Galaxiidae)
Galaxias platei, es un pez endémico de Chile y cubre una extensa área geográfica desde la zona centro-sur hasta gran parte de la Patagonia (38ºS-54ºS), incluyendo también parte de Argentina. En este trabajo se determinó el contenido somático de ADN nuclear (valor 2C) de Galaxias platei (Galaxiidae) mediante microdensitometría nuclear de eritrocitos sometidos a tinción de Feulgen. El valor 2C de G. platei es 1,88±0,16 pg y su valor C es equivalente a 0,94 pg (921,2 pMb). El valor C de G. platei está dentro del rango descrito para otras especies de Osmeriformes (valores entre 0,62 y 3,2 pg) y es menor al valor documentado previamente para G. maculatus (C = 1,105 pg). Estos datos contribuyen a incrementar los antecedentes genómicos disponibles para el género Galaxias los que, en conjunto con los resultados de análisis cromosómicos previos, podrían ser útiles para evaluar aquellas relaciones genéricas y específicas que han sido propuestas para la familia Galaxiidae.
C-banding pattern in the geophytic Leontochir ovallei (Alstroemeriaceae)
The monotypic genus Leontochir Phil. (Alstroemeriaceae Dumortier), represented by Leontochir ovallei, is endemic to Chile, and its geographical distribution is restricted to the coastal zone of the Atacama Desert (28°S). In previous cytogenetic studies on L. ovallei a diploid karyotype 2n = 2x = 18 was described. In this work a first analysis of the C-banding pattern of L. ovallei is presented. L. ovallei showed large regions of constitutive heterochromatin within the karyotype, with C-bands on all chromosome pairs except 9. The relative length of the C-bands was 20.0% of the total haploid set length. The presence of large regions of constitutive heterochromatin on the chromosomes was concurrent with the presence of many conspicuous and large chromocenters in the interphase nuclei. According to these results, L. ovallei shows the largest value of relative C-band length so far described within the Alstroemeriaceae. These cytogenetic results on L. ovallei increase the available data on C-banding patterns in Alstroemeriaceae with an additional genus.
Gonadal organization and gametogenesis in musculium argentinum (Veneroida: Sphaeriidae) from a population in Southern Chile
The gonadal organization and cytological characteristics of gametogenesis in a population of the freshwater clam Musculium argentinum (d'Orbigny, 1835) are described. Sections of the rather small gonad demonstrate the existence of hermaphroditic specimens, and is composed of hermaphrodite follicles among the intestine coils in the posterior dorsal region of the body. Follicles contain male and female germ cells at different stages of maturation, which can be recognized by their shape, size, and nuclear features. Male germ cells are organized in cysts, and spermatocytes do carry out meiosis. Within follicles, male and female germ cells occupy different regions. Gonad activity throughout the year is coincident with the life cycle pattern of the M. argentinum population studied previously.
Comparative karyology of lentic and lotic populations of Diplodon chilensis chilensis (Bivalvia: Hyriidae)
The mean karyotypes of four populations of Diplodon chilensis chilensis (Gray, 1828) (two lentic and two lotic) inhabiting the south of Chile are described and compared. Chromosomes were obtained by squash of cleaving embryos, previously treated with colchicine, fixed in ethanol-acetic acid 3:1 at 4°C, and stained using the Feulgen reaction. The karyotype of the four populations is 2n = 34, with metacentric and submetacentric chromosomes. In the population from the Peu-Peu stream, the centromeric position in two chromosome pairs (3 and 10) differs significantly from that in the corresponding pairs from the other populations. Karyotype findings of this study do not support the proposal that the differences described between lentic and lotic populations of D. ch. chilensis may result from genetic differentiation among populations. This study is an initial contribution to the knowledge of cytogenetic characteristics in Chilean populations of Diplodon chilensis chilensis.
Karyological study in the chilean rhatany Krameria cistoidea Hook. & Arn. (Krameriaceae)
The karyotype of the plant species Krameria cistoidea Hook. & Arn. was studied by assessing chromosome characters such as morphology, size, and C-banding pattern. The karyotype of K. cistoidea was composed only by metacentric chromosomes in the two populations studied. The haploid set length was 51.9±2.3 µm and the mean chromosome size was 8.68±0.78 µm. Some similarities in chromosome morphology and size can be observed among K. cistoidea and K. triandra, in addition to the chromosome number 2n=12 which is conserved within the genus. K. cistoidea exhibited a symmetric banding pattern with large C-bands in the telomeres of the short and long arms of all chromosomes, except the short arm of pair 1. The relative length of the C-bands was 23.5% of the total haploid set length. These cytological results on K. cistoidea are the first data on quantitative karyotype morphology and C-banding patterns in the genus Krameria