Sexing of Half-embryos Produced by Microsurgical Bisection of Mouse Morulae and Production of Chimeric Mouse of Defined Sex Composition by Aggregating Two Sexed Half-embryos

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Abstract
Using the halved morulae of mice obtained with microsurgical technique, the following two experiments were performed. Sexing of half-embryos by chromosomal analysis and transfer of the half-embryos after determining the sex of the other monozygotic half. One half of the bisected embryo was cultured in Colcemid solution (0.04 .mu.g/ml) to be ensured for chromosomal preparation. More than 50% (152/270) of the blastulated embryos from the halves could be sexed by direct sex chromosome analysis. Thirty-nine of the half-embryos of which the co-twin halves were sexed, were transplanted into the uterine horns of 18 pseudopregnant mice, and twelve became pregnant. The autopsies of them on Day 18 to 20 pregnancy, revealed the presence of 16 fetuses. The morphological sex of these fetuses thus obtained coincided completely with the previous judgment based on the chromosomal sexing. Production of chimeras of defined sex composition by aggregating two half-morulae of defined sex. Out of 147 pairs of half-morulae of two different strains (ICR and C3H/He), which were replaced in pairs into empty zona pellucidae, 107 (72.8%) were aggregated sucessfully and developed in vitro into full expanding blastocysts of typical form. Among the 107 aggregate blastocysts, 31 were sexed for both component embryos by chromosomal analysis on the co-twin half-embryos. When these 31 blastocysts were transferred, 11 living offspring including 4 chimeras were obtained. Transfer of 12 .male..tautm. .male. and 5 .female. .tautm. .female. aggregate blastocysts resulted in 8 males and 1 female, respectively. As a result of transfer of 14 .male. .tautm. .female. aggregate blastocysts, 1 male of chimeric phenotype and 1 female of albino; "single-type" offspring were obtained.

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