ABSTRACT
Approximately 90 species in the genus Leporinus (Characiformes, Anostomidae) are known, and most of them do not present differentiated sex chromosomes. However, there is a group of 7 species that share a heteromorphic ZW sex system. In all of these species, the W chromosome is the largest one in the karyotype and is mostly heterochromatic. We investigated the distribution of several microsatellites in the genome of 4 Leporinus species that possess ZW chromosomes. Our results showed a very large accumulation of mostly microsatellites on the W chromosomes. This finding supports the presence of an interconnection between heterochromatinization and the accumulation of repetitive sequences, which has been proposed for sex chromosome evolution, and suggests that heterochromatinization is the earlier of the 2 processes. In spite of the common origin that has been proposed for W chromosomes in all of the studied species, the microsatellites followed different evolutionary trajectories in each species, which indicates a high plasticity for sex chromosome differentiation.
Subject(s)
Characiformes/genetics , Chromosome Mapping/methods , Microsatellite Repeats/genetics , Sex Chromosomes/genetics , Animals , Brazil , Female , Heterochromatin/genetics , Heterochromatin/ultrastructure , In Situ Hybridization, Fluorescence , Male , Sex Chromosomes/ultrastructure , Species SpecificityABSTRACT
A new type of airway has been widely used for two years, throughout hospitals in the United Kingdom. Designed and created since 1983 by Dr AIJ Brain, the Laryngeal Mask Airway (LMA) is a compromise between the endotracheal tube and the face-mask. Blindly inserted in an anaesthetized patient, without either a laryngoscope or neuromuscular blockade, it provides a good airway in almost all cases. It is often able to offer an effective alternative to difficult intubation. The LMA can be used with either spontaneous or positive pressure ventilation. Because it doesn't provide a reliable protection of the airway from aspiration, it should never be used in the patient with a full stomach. The spontaneously breathing patient, undergoing elective surgery for 15 to 60 minutes, in supine position, who would ordinarily be managed with a face-mask is the more likely candidate for the LMA. But, longer procedures, in lateral or prone position, with controlled ventilation can usually be carried out using the Brain's device. More effective and less demanding than the facial-mask, much less hurtful than the endotracheal tube, the Laryngeal Mask is potentially an important and valuable addition to anaesthetic care.
