Male meiotic segregation analyses of peri- and paracentric inversions in the pig species.

Inversions are well-known structural chromosomal rearrangements in humans and pigs. Such rearrangements generally have no effect on the carriers' phenotype. However, the presence of an inversion can lead to spermatogenesis impairments and to the production of unbalanced (recombinant) gametes, responsible for early miscarriages, stillbirth, or congenital abnormalities. Sperm samples from boars heterozygote for pericentric inv(2)(p1.1;q1.1), inv(2) (p1.1;q2.1), inv(1)(p2.1;q2.10), or inv(1)(p2.4;q2.9), as well as for paracentric inv(2)(q1.3;q2.5) or inv(1)(q1.2;q2.4) were analyzed using sperm FISH (fluorescent in situ hybridization on decondensed sperm heads) to determine the male meiotic segregation profiles of the rearrangements. Furthermore, the availability of sperm samples for 2 unrelated carriers of inv(2)(p1.1;q1.1) allowed us to check for the occurrence of inter-individual variability of the rates of unbalanced meiotic products for this rearrangement. The estimated proportions of recombinant gametes were very low for all the inversions studied (0.62%, 1.30%, 3.05%, 1.27%, 4.12% and 0.84%, respectively), albeit significantly higher than the control. The rearrangements should therefore have very little impact on the reproductive performance of the carriers. No difference was found between the 2 carriers of inv(2)(p1.1;q1.1), suggesting a lack of inter-individual variability for this rearrangement. Overall, no significant correlation was found between the sizes of the inverted fragments and the proportions of recombinant (unbalanced) gametes for the 6 inversions studied. This is in contradiction with most human results. Further studies (pairing and recombination analysis using immunostaining techniques) should be carried out to elucidate the origin of such an inter-species difference.

Study of inter- and intra-individual variation of meiotic segregation patterns in t(3;15)(q27;q13) boars.

Constitutional chromosomal rearrangements are relatively frequent genetic anomalies in both man and pigs. Among them, reciprocal translocations, present a specific meiotic segregation pattern. The potential "individual" effect of the t(3;15)(q27,q13) translocation was studied using SpermFISH to analyze the meiotic segregation patterns of three boars carrying this rearrangement. Three samples were taken at different times from one of these boars to analyze a potential "time" effect. No "time" or "individual" effect was found in this study. These results should allow more efficient management of certain reciprocal translocations in pig populations but need to be completed by the study of other kinds of chromosomal rearrangements.