710 



SPERM, OVA, AND PREGNANCY 



concentrations of monovalent cations (Na+ 

 and K+), modifications which might ac- 

 count for the increase in capacity for move- 

 ment of sperm at this stage in their develop- 

 mental history. Unpublished observations of 

 electron micrographs of human sperm by 

 Fawcett indicate that the midpiece may 

 undergo further significant alterations after 

 spermatogenesis, changes which involve par- 

 ticularly the mitochondrial sheath and the 

 annulus at the junction of the midpiece and 

 principal piece of the flagellum. 



In the female genital tract, further sperm 

 modifications occur which appear to be nec- 

 essary for fertilization. A period of incuba- 

 tion in the tubal fluids is required during 

 which changes (capacitation) occur that 

 seem to involve both enzymatic and struc- 

 tural properties of the sperm (Austin and 

 Bishop, 1958a; Chang, 1958; Noyes, 1959b t. 

 During this 2- to 6-hour interval, the sperm, 

 at least of the rat, hamster, and rabbit, un- 

 dergo certain changes in the head, which in- 

 clude loss of the "galea capitis" and partial 

 dissolution of the acrosome. 



What other changes occur in spermatozoa, 

 in vivo, during their transport through the 

 genital tracts, and of what consequence 

 such modifications are to either survival or 

 fertilization can only be surmised. In some 

 respects, the metabolic properties of epi- 

 didymal and seminal sperm differ, as studied 

 in vitro (see Metabolism). Pronounced 

 changes, of course, follow activation at the 

 time of ejaculation, changes associated with 

 energy production and motility. Other bio- 

 chemical activities are believed to occur, 

 moreover, which may be regarded as part of 

 the "resting" metabolism of sperm. This 

 will be discussed in a later section. On the 

 other hand, certain deleterious changes may 

 also take place, particularly during sperm 

 storage, to such an extent that large molecu- 

 lar moieties, such as cytochrome c, are ap- 

 parently lost from both bull and ram sper- 

 matozoa (Mann, 1954). 



B. CYTOGENETIC DIFFERENCES IN SPERM 



As the result of meiosis and segregation, 

 spermatozoa are haploid in chromosome 

 number and bear one-half of the hereditary 

 complement which is carried into the next 

 generation at fertilization. The two main 



types of sperm, X- and Y-bearing (in mam- 

 mals), are responsible for female and male 

 offspring, respectively, on union with the 

 X-chromosome egg. Attempts have indeed 

 been made, with questionable success, to 

 separate these two kinds of sperm both by 

 electrophoretic (Schroder, 194:0a, b, 1941a, 

 b, 1944; Gordon, 1957) and by countercur- 

 rent centrifugal methods (Lindahl, 1956). 



Genetically distinct spermatozoa were 

 long ago demonstrated by Landsteiner and 

 Levine (1926), who showed that the A and 

 B blood-group antigens occur in human 

 sperm, without, however, making clear 

 whether the specific phenotype of a given 

 sperm is determined by its haploid set of 

 genes or by the diploid set of the spermato- 

 cyte from which it is derived. GuUbring 

 (1957) has recently revived this issue and 

 claims that the A and B antigens occur on 

 separate sperm produced by a heterozygous 

 AB blood-group male. Further evidence of 

 gene-induced sperm heterogeneity is af- 

 forded by the work of Beatty (1956), who 

 studied the 3,4-dihydroxyphenylalanine 

 (DOPA) reaction in sperm from pigmented 

 and pale rabbits. A high correlation was 

 found between the melanizing activity of 

 the spermatozoa and the depth of coat color 

 of the rabbits from which they came. It will 

 be remembered that Snell (1944) found sig- 

 nificant antigenic differences in the sperm 

 of inbred strains of mice, those of strain C 

 being readily distinguishable from those of 

 strain C57 on a basis of their agglutination 

 with specific antisera. Braden (1956, 1958a, 

 1959) has recently made an intensive study 

 of sperm variation in pure strains of mice. 

 Statistically significant differences in size 

 and shape of the sperm head were demon- 

 strated in the four inbred lines, CBA, 

 C57BL, A, and RIII. IVIoreover, at fertiliza- 

 tion, strain differences become apparent in 

 the tendency for more than one sperm to 

 penetrate the egg membranes, sperm of 

 strain C57BL, for example, showing a sig- 

 nificantly higher percentage (26 per cent) 

 than those of other strains (12 to 14 per 

 cent). Further, Braden (1958b) has found 

 abnormalities in the segregation ratio of 

 mice which tend to indicate that the actual 

 allele present (e.g., at the T-locus) in the 

 sperm determines certain of its properties. 



