THE DNA CONTENT OF SPERMATOZOA FROM DIFFERENT STRAINS OF MICE

Certain morphological characters of mammalian spermatozoa have been shown to have a high heritability (Beatty, 1970). Sperm dimensions may be altered by genetic selection (Woolley, 1970). In addition to the biological action ofthe genes, the actual mass of the DNA and proteins, which constitute the major components of the head, may affect the sperm phenotype. Unlike genetically active cells in which nuclear size is governed, to a certain extent, by metabolic factors, the sperm genome is condensed, homogeneous and inactive. It might therefore be expected that head size would be influenced both by the quantity of DNA present and by the way it is condensed. Thus diploid spermatozoa have enlarged heads (Beatty & Fechheimer, 1972), whereas spermatozoa with abnormally small heads might have a lower Feulgen\p=m-\DNAcontent than morphologically normal members of the same ejaculate (Gledhill, 1970). The size differences described in the latter studies probably reflect alterations in sperm chromatin structure affecting the availability of Feulgen-reactive sites. When the DNA contents of small and normal spermatozoa were compared by ultraviolet(u.v.) absorption methods, no significant differences were observed (Gledhill