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Cytogenetic studies enable the identification and early elimination from breeding of animals affected by hereditary karyotype defects. These defects cause developmental disorders and a significant decrease of fertility parameters (from a few dozen to 100%) and productivity of breeding herds, and consequently measurable financial losses. Due to the potential possibility of spontaneous occurrence of chromosomal aberrations and rapid spreading of these genetic defects in the population, especially in the conditions of the use of artificial insemination, it is necessary to carry out regular karyotype control of breeding animals. Cytogenetic monitoring of cattle qualified for reproduction guarantees the systematic identification of all karyotype abnormalities carriers, which, causing the decrease of fertility or sterility, determine the low reproductive performance of animals affected by these defects. The cytogenetic control system, implemented by the use of constantly perfected cytomolecular techniques, enables a very precise, reliable evaluation of karyotype and diagnosis of chromosomal abnormalities, as well as formulation of specific recommendations for culling.
The aim of this work was to assess the meiosis process in bulls on the basis of observations of the X-Y bivalent. The assessment was made using FISH technique in successive stages of the meiotic division. Gonad specimens were taken postmortem from three Red-and-White Lowland bulls that had originated from the Experimental Station Ltd of the National Research Institute of Animal Production in Grodziec Śląski. The animals were chosen on account of their semen parameters, which were lower than herd average. Meiotic chromosome preparations were made as described by Evans in 1964. Hybridization was carried out using molecular probes that identify bull X and Y chromosomes. A total of 38 spermatogonia and 144 primary spermatocytes at different stages of the meiotic division were tested. The analysis of hybridization signals (red-purple indicating the Y chromosome and yellow indicating the X chromosome) in bull gonad cells did not show any abnormalities in the meiosis process. A 90% dissociated X-Y bivalent was only observed in five spermatocytes at metaphase I. It is therefore concluded that these minor changes did not lower the semen parameters of the investigated animals.
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