A two-step polymerase chain reaction (PCR) assay was used to determine the sex of mouse preimplantation embryos obtained from oocytes fertilized and cultured in vitro, to investigate the differences in the developmental rates of mouse embryos according to the sex. All the in vitro developed embryos could be analyzed by this method. When the embryos were classified according to the time of morula to blastocyst transition as fast-intermediate- and slow-growing embryos, a significantly high percentage (78.0%) of the fast-developing embryos were identified as males; while a significantly lower percentage (42.5%) of slow-developing embryos were identified as males. The intermediate-developing embryos presented a sex ratio not significantly different from the total (57.5%). The deviation of sex ratio was further confirmed by embryo transfer experiment, where fast- and slow-developing embryos gave 76.2% and 25.7% male fetuses, respectively. We concluded that male mouse embryos fertilized and cultured in vitro develop faster than female embryos.

The system reported here describes selective, exhaustive, and nonredundant generation and counting algorithms for acyclic connectivity isomers associated with any molecular formula. Isomer structures can have multiple bonds and heteroatoms with mixed valences, as in the case of thiosulfonic acids. Structural isomer characteristics (IC) for each molecular formula are determined according to an expression derived from basic graph principles. The generation process uses a tuple notation and the concept of lexicographic order (see ref 13) and is done in three steps: (i) generation of the skeleton of the acyclic structure; (ii) incorporation of heteroatoms to the structure; (iii) incorporation of multiple bonds. Isomer redundant filtering processes and algorithms for doing a single-or a multiple-pattern restriction over the structures to be generated were developed. The code describing the generated isomers is compact and allows for both efficient molecular database storage and interaction with a graphic interface and with different calculation modules of CAMD such as those of topological indexes, molecular volume, and other molecular properties derived from semiempirical and ab initio methods. The system is therefore of great utility in structure elucidation, in organic synthesis, and especially in molecular design.

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