Lack of pairing loop formation in synaptonemal complex preparation of a boar carrying an inversion

Breeding and Economic Aspects of Cytogenetic Screening Studies of Pigs Qualified for Reproduction

Cytogenetic monitoring allows the identification and early removal of pigs affected by inherited karyotype defects from breeding herds. These abnormalities cause developmental anomalies, considerably reducing the fertility (by several dozen to 100%) and performance parameters of breeding herds, resulting in substantial financial losses. This mainly concerns reciprocal translocations, typical of pigs, which are highly prevalent (about 0.46%), generally occur de novo, and normally result in low breeding soundness of the carriers. Due to the potential spontaneous occurrence of chromosomal aberrations and the rapid spread of these genetic defects in the population, especially under artificial insemination conditions, it is necessary to perform routine karyotype screening of animals qualified for reproduction. The cytogenetic screening program for young boars, carried out using continually refined diagnostic techniques, permits a precise and reliable karyotype assessment, identification of chromosomal abnormalities, and formulation of specific selection guidelines.

EM studies of female meiosis in wood lemmings with different sex chromosome constitutions

The chromosomes were studied throughout meiotic prophase by electron microscopy of surface-spread oocytes from one XX, four X*X, and three X*Y female wood lemmings, Myopus schisticolor. The X* chromosome had originated from X by a deletion and an inversion in the short arm. The deletion was confirmed in pachytene cells from X*X females; a D-loop was present in the sex bivalent in 16.8% of the cells, and asynapsis of unequal ends was seen in 9.1% of other cells. At late pachytene the D-loop underwent synaptic adjustment. The breakpoints of the deletion are in G-light bands. No inversion loop was seen, which also is in agreement with Ashley's ('88) hypothesis; at least one of the presumed breakpoints of the inversion is in G-dark chromatin. Various types of synaptic abnormalities, such as nonhomologous pairing (triple pairing, interchange, self-synapsis), univalents, foldbacks, and broken lateral elements, were encountered in all types of female. X*Y females showed a high frequency of abnormal oocytes (70.7%), which significantly exceeded that of X*X (23.1%) and XX (8.1%). Univalents were particularly common in the X*Y females. J. Exp. Zool. 290:504-516, 2001.