[The reproductive performance of XX/XY male chimeric mice]

The reproductive performance of male aggregation chimeric mice was examined. C57BL/6 in equilibrium BALB/c male chimeras and control animals, C57BL/6, BALB/c, and their reciprocal F1 crosses, were mated with ICR females. Of 45 overt chimeras, 13 produced mixed-genotype progenies and were revealed to be XY/XY chimeras. By karyotype analysis 16 of 32 single-genotype progeny chimeras were determined to be XX/XY chimeras, but the remaining single-genotype progeny chimeras showed only XY metaphase plates, so that their chromosomal sex could not be determined. The mean litter size of C57BL/6 was significantly higher than that of BALB/c. In contrast, the birth rate of C57BL/6 was lower than that of BALB/c. XY/XY chimeras showed almost the same performance as C57BL/6 for litter size and as BALB/c for birth rate. There were no significant differences for both traits between the reciprocal F1 crosses and XY/XY chimeras. The mean litter size of XX/XY chimeras was lower than that of XY/XY chimeras and the differences was statistically significant. Some XX/XY chimeras had very small testes, while XY/XY chimeras had normal testes. Such results indicate that the reproductive performance of XX/XY male chimeras is inferior to that of XY/XY males.