DETECTION OF MOSAIC AND NON-MOSAIC CHROMOSOME-ABNORMALITIES IN 6 TO 8-DAY-OLD HUMAN BLASTOCYSTS

A reliable technique has been developed for the production of good qua lity G-banded chromosome preparations from 6- to 8-day-old human blast ocysts (20-800 cell stage) from an in vitro fertilization programme. T he technique involves a thymidine cell division synchronization step t o reduce the exposure time to colcemid, in conjunction with a simple 7 0% acetic acid disaggregation procedure to produce discrete metaphases for analysis. Of 105 blastocysts processed by this technique, 9 were lost during handling and 10 showed no dividing cells. The remaining 86 produced useful separate metaphases with a mean mitotic activity of 6 .5%. A full G-banded karyotype was obtained from 1-6 cells in 55 blast ocysts (64%), incomplete G-banded analysis but with full information o f ploidy was obtained from 18 blastocysts (21%), with 13 (15%) produci ng no useful cytogenetic results. Abnormalities observed included poly ploidy, diploid/polyploid mosaicism, non-mosaic trisomy 16 (2 cases), 46,Xdel(X)-(q21)/46,XX (1 case) and several single cells with trisomie s or structural anomalies in other-wise normal blastocysts. Variable l evels of structural chromosome damage, with apparent interchanges, chr omosome branching and anomalous chromatid pairing were also seen.