ABSTRACT
ABSTRACT The present review aims to summarize the research carried out in relation to meiosis in birds, especially by observing the protein axes of the chromosomes in prophase I of meiosis. This line of research, initially developed in Argentina, has provided key data in the study of the evolution of sex chromosomes and the mechanisms involved in the frequency and distribution of crossing over in birds, among other topics. Some of these contributions, in addition to those made by other authors, are described also providing the general theoretical framework or the hypotheses that support them.
RESUMEN La presente revisión tiene por objetivo resumir las investigaciones realizadas en relación a la meiosis de las aves, especialmente mediante la observación de los ejes proteicos de los cromosomas en la profase I de la meiosis. Esta línea de investigación, desarrollada inicialmente en Argentina, ha aportado datos clave dentro del estudio de la evolución de los cromosomas sexuales y los mecanismos involucrados en la frecuencia y distribución del crossing over en las aves, entre otros temas. Algunas de estas contribuciones, además de las realizadas por otros autores, se describen proporcionando también el marco teórico general o las hipótesis que las sustentan.
ABSTRACT
A testicu1ar biopsy from an infertile man carrying a heterozygous chromosome translocation t(ll; 14) was studied with synaptonemal complex analysis and immunolocalization of the protein MLH 1 for crossover detection. A full blockage of spermatogenesis at the spermatocyte stage was related to the presence of the translocation quadrivalents at pachytene. Only 2% of the quadrivalents showed full synapsis. Most of the spermatocytes showed asynaptic free ends that frequently mingled with the XY pair. The average number of crossovers per cell was diminished from a mean of 52.7 in controls to a mean of 48 in the patient. The difference between the number of crossovers in the quadrivalent and the normal bivalents was highly significant. The distribution of crossovers over the segment of the quadrivalent corresponding to bivalent #14 was also very different from that ofthe control. It is concluded that in this translocation, the pattern of crossovers is changed, mainly due to a synaptic hindrance in the quadrivalent, and that the spermatogenesis arrest is mainly due to the quadrivalents that interact with the XY pair
Subject(s)
Male , Humans , /genetics , /genetics , Spermatogenesis/physiology , Spermatogenesis/genetics , Infertility, Male/diagnosis , Infertility, Male/genetics , Infertility, Male/pathology , Meiosis/genetics , Chromosome Aberrations , Chromosome Disorders/diagnosis , Chromosome Disorders/genetics , Chromosome Disorders/pathologyABSTRACT
A scheme is proposed to explain the process of sex chromosome differentiation in the class Aves. It is based on the restriction of recombination in an ancestral homomorphic ZW pair and the subsequent degeneration of the non-recombining region of the W chromosome leading to the highly heteromorphic sex chromosomes of carinate birds. The model presented here and Ohno's model of sex chromosome differentiation in Ophidia are the only integral models of sex chromosome evolution based on cytological evidences. The co-existence among living birds of mostly homomorphic (Ratites) and highly heteromorphic ZW pairs (carinates) provides a unique ground to study the mechanisms of sex chromosome differentiation in vertebrates
Subject(s)
Animals , Biological Evolution , Birds , Sex ChromosomesABSTRACT
Recombination nodules are submicroscopic structures that are found in all the sexually reproducing, eukaryotic organisms during the pachytene stage of meiotic prophase I. Despite many reports on their number and location, no definite substructure was previously reported in these nodules. The present observations on spread oocytes and spermatocytes of the pigeon, using an improved technique for protein preservation, shown the presence of particulate subunits or "recombinomeres" in late recombination nodules, besides an interparticle matrix. The number of subunits per each nodule ranges from 1 to 5, and this number increases with the advancement of pachytene substages. These subunits are present in recombination nodules of all the other avian species previously studied, and they may be present in other organisms as well. It is suggested that the particulate substructure of recombination nodules mirrors the multiplicity of multienzymatic complexes that are needed for the ordered series of reactions that occur at the molecular level in the sites of meiotic recombination