GENETICS OF ABNORMAL HUMAN FERTILIZATION

The purpose of this study was to assess the genetic status of abnormal zygotes following assisted fertilization. Dispermic, monopronucleated and digynic zygotes were allowed to cleave intact or after enucleatio n, and on the biopsied blastomeres, multiplex polymerase chain reactio n and fluorescent in-situ hybridization were performed. It was found t hat the distal pronucleus was usually male in origin in dispermic embr yos, and that the ses ratio was restored when they were enucleated; ho wever, they became mosaic at metaphase and their genetic heterogeneity was not restored after enucleation. Monopronucleated zygotes derived from standard in-vitro insemination can be transferred to the patient, since they usually showed normal diploid complement in their cells. O n the contrary, single-pronucleated zygotes derived from intracytoplas mic sperm injection were usually activated parthenogenetically, but no t fertilized. Digynic embryos, unlike dispermic ones, had a very low i ncidence of mosaicism, and when present, such mosaicism originated at a later embryo division. Most of the digynic embryos were triploid, in dicating that the first division was normal and bipolar; moreover, whe n the female pronucleus was removed, they became diploid and their gen etic status was considered normal, The recognition and understanding o f fertilization abnormalities allow the identification of methods lead ing to their avoidance or correction.