Reciprocal translocations: tracing their meiotic behavior

Purpose: Segregation and interchromosomal effect studies have been performed in reciprocal translocation carriers by sperm-fluorescent in situ hybridization reporting a great heterogeneity. The divergences have been attributed to the particular cytogenetic characteristics of each rearrangement. Nevertheless, there is no consensus in the factors that are responsible for such variability. The purpose of this study was to determine which cytogenetic features influence in the segregation and interchromosomal effect outcome. Methods: Segregation and interchromosomal effects analyses were performed in 14 reciprocal translocation carriers, selected because they presented very different cytogenetic features regarding the tetravalent pairing geometry. In each segregation study, a customized combination of probes was used to identify all the segregation products. In the interchromosomal effect study, we used a triple-color fluorescent in situ hybridization for chromosomes X, Y, and 18. Results: A preferential segregation pattern with a gradually decreasing production of Alternate, Adjacent 1, Adjacent 11, and 3:1 segregation was observed in the segregation analysis. Some specific features have been observed to influence this distribution: size of the translocated and centric segments and the presence of centromeres from acrocentric chromosomes in the center of the cross. Aneuploidy/diploidy screening revealed increased frequencies of numerical anomalies in seven carriers. Conclusions: Our data suggest that reciprocal translocations display a more homogeneous behavior than described in the literature. The interchromosomal effects represent an additional source of imbalances in these carriers. Genet Med 2008:10(10):730-738.