Characterization of a translocation and its impact on fertility in the pig.

A chromosome anomaly originally detected in two intersex pigs and previously reported as a Robertsonian translocation was characterized, and its transmission pattern was assessed by analyzing the progeny and immediate relatives of a sow. Cytogenetic investigations on four phenotypically normal relatives of the intersexes, including a sow, showed that the rearrangement was a reciprocal translocation involving the X chromosome and an autosome. Giemsa-banding and reverse-banding techniques indicated that the break in the X chromosome may have occurred in the terminal segment of the short arm (Xp) and that in the autosome in the proximal segment of the acrocentric chromosome 14 (14q). Reverse-banding techniques also revealed that the normal X is the late-replicating X in female translocation carriers. Centromere banding revealed an intercalary band on the long arm of the submetacentric chromosome representing the altered X in translocation carriers. The translocation was designated as rcp (X;14) (p+;q-). Chromosome analysis on 45 of 72 live offspring of the carrier sow showed a 20:25 distribution of carriers to normal piglets, with a carrier to normal ratio of 5:13 among females and 15:12 among male piglets, indicating an overall reduction of females (18) compared with males (27). Male carriers from one litter at sexual maturity showed hypoplastic testes and no spermatozoa in their ejaculates or fluid aspirates from the cauda epididymis. Their seminiferous tubules were narrow, spermatogenesis was impaired, and pyknotic and giant nuclei were abundant in the germinal epithelium. Meiotic preparations showed no stage beyond pachytene, suggesting that the absence of spermatozoa in the ejaculates may be due to the arrest of cells at the pachytene stage.