GENETIC INCOMPATIBILITY BETWEEN X-LINKED LOCI AND TWO AUTOSOMAL REGIONS CAUSES HYBRID BREAKDOWN BETWEEN TWO MOUSE SUBSPECIES

Hybrid breakdown is a type of reproductive failure that appears after F2 generation of crosses between different species or subspecies. It is caused by incompatibility between alleles of interacting genes. We have studied the hybrid breakdown using a consomic strain, C57BL/6J-XM5M, in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M. m. molossinus). Males of this consomic strain are sterile due to the abnormal sperm head morphology, whereas F, hybrids between C57BL/6J and MSM/Ms are completely fertile. This finding implies that incompatibility between X-linked gene(s) and other chromosomal gene(s) causes the hybrid breakdown observed in C57BL/6J-XMSM. The previous our study revealed that at least three X-linked QTLs are responsible for the sperm head abnormality and the hybrid breakdown. We conducted the whole-genome scan to detect autosomal and/or Y-chromosomal regions, which interact with the X-linked QTLs and underlie the genetic incompatibility. The result suggested that Chromosome 1 and 11 interact with the X-linked QTLs for proper male reproduction in parental MSM/Ms strain, and disruption of this interaction causes the hybrid breakdown.