Recently developed staining techniques have made it possible to recognize the Y and number 9 chromosome in human spermatozoan heads. Thus, the frequency of numerical aberrations involving these two chromsomes has become amenable to investigation in sperm.
Y Chromosome. It is well established that the distal portion of the human Y chromosome at metaphase fluoresces more intensely than the rest of the karyotype after quinacrine staining (Caspersson et al., 1970). By this property the presence of the Y chromosome can also be demonstrated in the interphase of somatic cells (Pearson et al., 1970) at meiosis (Pearson and Bobrow, 1970) and in mature spermatozoa (Barlow and Vosa, 1970).
The objective of the present study (Pawlowitzki and Pearson, 1971) was to count spermatozoa with two Y bodies in a series of fertile men in order to estimate the frequency of meiotic errors involving the Y chromosome in the normal male population.
A total of 10.692 spermatozoa obtained from ejaculates of 12 normal fertile healthy males were examined. 5 of these (individuals No. 7--t2, Table t) were donors of a sperm bank 1, their semen had been stored for periods up to several months in liquid nitrogen at temperatures of ~--190Β°C before investigation. The technique of the fluorescent examination (Pearson and Bobrow, 1970) and the criteria of counting sperm and fluorescent bodies (Pawlowitzki, Habflitationsschrift, 1971) were described elsewere in detail.
The results are shown in the table: 54.6% of the examined spermatozoa had no fluorescent body, presumably being X bearing sperm. In 43.9% a single fluorescent body was seen, which are considered to be Y bearing sperm. 1.3% had 2 fluorescent bodies and therefore are believed to contain a supernumerary Y chromosome. Giant forms with 2 fluorescent bodies (0.2%) were counted separately, since these may be polyploid (Sumner, 1971;Pawlowitzki and Bosse, 1972). The contribution of polyploidy to sperm with doubled Y bodies appears to be about 1 in 7.
Our results on the frequency of YY gametes in healthy fertile men are in good agreement with the results of other studies: Pearson and Bobrow (1970) found 1.4% spermatids with 2 fluorescent bodies each in testicular tissue of 3 normal