Y chromosome visibility in quinacrine-stained human spermatozoa

Abstract

THE fluorescent dye, quinacrine, binds strongly to the Y chromosome and only to a lesser extent to the other chromosomes in human metaphase cell preparations¹. A bright fluorescent spot (F body), which is presumed to be the Y chromosome, is clearly visible in stained interphase cells from various tissues from the human male^2–5 and in mature spermatozoa^6,7. Spermatozoa bearing one F body (about 45 % of the total) are taken to be Y spermatozoa, and the staining method is now being used widely to detect physical differences, for example, in DNA content and head size^7,8 and motility⁹ between X and Y spermatozoa, and for testing the efficiency of procedures designed to separate them^10–13. Spermatozoa bearing two F bodies (about 1.3% of the total) have been interpreted as YY spermatozoa^7,8, and the relatively high number of such spermatozoa has led to speculation concerning the seemingly high non-disjunction rates during spermatogenesis^8,14,15. We here examine the factors which affect Y chromosome visibility in sperm heads, and conclude that the F body count depends critically on observer performance, that the presence of YY spermatozoa cannot be demonstrated decisively using the quinacrine stain, and that measured physical differences between spermatozoa with and without an F body may partly reflect a dependence of the Y chromosome detection efficiency on the size of the sperm head.