Human Non-Clinical Genetics
Or ig inal ly , the frequency of aneuploidy was estimated f r o m cytogenetic studies on spontaneous miscarriages and estimates of the real underlying frequency were attempted by extrapolating f r o m these measurements. Techniques have n o w been developed to measure the frequency of aneuploidy directly i n the gametes. The first reliable technique involved fusing h u m a n sperm w i t h Chinese hamster oocytes after w h i c h the number of h u m a n chromosomes in the sperm could be visualized (Rudak etal., 1978; M a r t i n et aL, 1991). However , the number of sperm analysed was l imited by the technical diff iculty of the procedure and , lately, greater progress has been made by using fluorescent molecular probes to analyse the chromosomes indirectly. Sperm w i t h an abnormal chromosome number can be detected because they possess an extra fluorescent spot corresponding to one extra chromosome. Fluorescent probes, w h i c h are specific for each chromosome, have been developed and so the frequency of extra chromosomes can be estimated separately for different chromosomes (Jacobs, 1992; Spriggs et ai, 1996). A l t h o u g h originally, and long before the development of the modern probes, the rel iabi l i ty of techniques w h i c h measured aneuploidy directly i n the gametes was questioned, the modern molecular methods are very specific for each chromosome and, consequently, the rel iabil i ty of the data is not in doubt ( M a r t i n & Rademaker, 1995).