Chromosomal segregation and recombination in human sperm cells from reciprocal translocation carriers

To determine whether recombination occurring around the breakpoints of translocated chromosomes may affect the accuracy of the current linkage analysis-based diagnosis of reciprocal translocation (RT) embryos.

Here, we have selected 688 single sperm cells sampled from 14 RT carriers with signed informed consent before semen collection and systematically investigated their chromosomal segregation patterns and potential recombination of translocated chromosomes.

We found that 39.96% of sperm cells showed alternative segregation patterns to produce normal and chromosomally balanced sperm cells, while 39.01% presented with an adjacent-1 segregation pattern, and 16.06% presented with an adjacent-2 segregation pattern, and 4.59% presented with a 3:1 segregation pattern. Moreover, we discovered a previously unknown segregation pattern at 0.38% occurrence. Notably, of the 887 recombination events on RT-associated chromosomes identified, 18 recombination events were located within the range of 5 Mb around breakpoints, among which 10/18 (55.6%) were located within 1-3 Mb of the breakpoint.

Our study provides evidence for recombination within the 5 Mb region flanking the breakpoints of translocated chromosomes, and these results suggest a non-negligible risk in the accurate diagnosis of chromosomal translocation in embryos through current linkage analysis-based diagnostic methods.