R. A. BEATTY
R. A. BEATTY
(1) Mixed insemination of known numbers of spermatozoa from two rabbits produced, spermatozoon for spermatozoon, offspring in the ratio of 1 :5. This difference in spermatozoan fertility was highly significant, and consistent over four experiments. It is thought to be a consequence of, and in turn a useful measure of, differences in the viability of spermatozoa in the original ejaculates. Such differences may be of common occurrence, and their existence would not necessarily be suspected from the records of natural matings. (2) The conception rate, or percentage of inseminations yielding a litter, was shown in one experiment to increase as the number of males contributing to the inseminate increased, even though the nett total number of spermatozoa per inseminate was held constant. These observations are not fully conclusive, but are presented as a recorded experimental finding of the type expected by certain Russian workers. (3) Inseminates from one particular male alone gave no offspring, but offspring fathered by this male appeared after mixed insemination, as if the fertility of its spermatozoa had been assisted by the admixture with other semen.
R. S. MATHUR and R. A. BEATTY
Quantitative estimations indicated the presence of DOPA oxidase (DOPA-OX), lactic dehydrogenase (LDH), malic dehydrogenase (MDH) and leucine aminopeptidase (LAP) in unwashed spermatozoa from the ductus deferentes of three inbred strains of mice (CBA, JBT and C57). Variations in enzyme activity attributable to a combination of age and strain effects were highly significant for all enzymes except MDH. There was one highly significant strain-specific difference, spermatozoa of C57 mice having about 2½ times the LDH activity of spermatozoa from CBA mice of comparable age. A-strain (albino) mice did not react for DOPA-OX whereas the three pigmented strains reacted positively. Strains which did not differ in mean enzyme activity were: CBA, C57, JBT (DOPA-OX); CBA, JBT (MDH).
A. D. CHROTHERS and R. A. BEATTY
The existence of polyploid mammalian spermatozoa has been inferred from studies of Feulgen-DNA absorption. Rabbit spermatozoa fell into two discrete groups with mean absorptions close to a 1:2 ratio (inferred to be haploids and diploids respectively) ; simple visual appraisal of the size of the head or nucleus gave an identical classification. The incidences of ploidy classes were 98·94% haploid, 1·06% diploid, 0·00% higher than diploid (N= 3010; from DNA measurements and visual appraisal of the size in a rabbit chosen to have a high incidence of diploids) and, correspondingly, 99·691%, 0·308%, 0·001% (N=138001; from sixty-nine unselected rabbits, scored by visual appraisal of the size of the sperm head). In man also, virtually discrete groups with absorptions close to a 1:2 ratio existed and were inferred to be haploids and diploids respectively. A few human spermatozoa were found with absorptions corresponding to a ploidy of three and/or four. Visual appraisal of the size of the human sperm nucleus as Small, Medium or Large was only a partial guide to ploidy. All Small human spermatozoa measured for DNA absorption were found to be haploid. About two-thirds of Medium human spermatozoa were found, however, to be haploid, and some Large spermatozoa were haploid or diploid. The incidences of ploidy classes in the human were 99·37% haploid, 0·56% diploid, 0·07% higher than diploid (N=5554; with consistency between duplicate slides and between two subjects; from DNA measurements and visual appraisal of nuclear size). The estimated incidence of diploid human spermatozoa is consistent with the known incidence of triploid fetuses. In a mouse with a putatively high incidence of diploids, all 1000 DNA measurements were nevertheless within the haploid range, with one diploid encountered outside the main sampling.
K. P. PANT and R. A. BEATTY
Transplantation of blastocysts from one inbred strain to another and consequent pre- and postnatal development with a different strain as mother has no apparent effect on sperm dimensions.
R. A. BEATTY and D. P. MUKHERJEE
In inbred male mice sampled at a standard time of year, increased age was accompanied by a marked fall in the proportion of spermatozoa with normal acrosomal caps, thus indicating a concomitant fall in fertility. Age trends were noted in the projected area of the midpiece and perhaps also in the breadth of the spermatozoan head. There was no significant age trend in the projected area of the spermatozoan head or the length of the midpiece. No difference of any kind was detected between the spermatozoa of albino and heterozygous albino males.
G. P. M. MOORE and R. A. BEATTY
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 of the 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—DNA content than morphologically normal members of the
N. E. SKAKKEBÆK and R. A. BEATTY
N. S. FECHHEIMER and R. A. BEATTY
Chromosomal analyses were made of 463 rabbit blastocysts drawn from thirty-nine superovulated does of four strains. Semen containing 1·5% diploid spermatozoa was taken from one strain only. Artificial insemination was conducted with untreated semen or with centrifuged fractions containing either 0·4% or 2·9% diploid spermatozoa. The results indicate that diploid spermatozoa are not a major cause of triploidy among embryos.
The sex ratio scored chromosomally among 434 diploid blastocysts was 48·62 (±2·40)% males. With data in the literature incorporated, the average sex ratio among 1077 blastocysts (consistent over three species of mammal) became 50·42 (±1·52)% males. These figures may be taken to estimate the primary sex ratio. Sex ratio among blastocysts is extremely stable over various biological and experimental conditions.
Twenty-three (5%) of the 463 analysable blastocysts were heteroploid. They comprised eight triploids (5 XXX, 3 XXY), four trisomics, four diploid/trisomic mosaics, one diploid/monosomic mosaic, four diploid/ tetraploid mosaics, one diploid/triploid mosaic and one triploid/ hexaploid mosaic. `Clustering' of heteroploids occurred in particular dams. Superovulation had no demonstrable effect on the incidence of heteroploidy. There is some evidence of genetic (dam strain) effects on the incidence.
R. A. Beatty, D. L. Stewart, R. L. Spooner and J. L. Hancock
A.R.C. Unit of Animal Genetics, Department of Genetics, West Mains Road, Edinburgh EH9 3JN, Ministry of Agriculture, Fisheries and Food, Cattle Breeding Centre, Shinfield, Reading RG2 9BZ, A.R.C. Cattle Blood-Typing Service, Animal Breeding Research Organization, West Mains Road, Edinburgh EH93JQ, and§Department of Anatomy, Royal Veterinary College, London NW1OTU, U.K.
This paper gives evidence that deep freezing depresses the fertility of the semen of different bulls unequally, that the period of time spent in the frozen state has no additional effect, and that replicate experiments with mixed (heterospermic) insemination give concordant results. The paper marks a further stage in an experiment with heterospermic insemination replicated over 6 successive weeks in December 1969-January 1970. In each replicate one semen mixture was made containing equal numbers of spermatozoa newly collected from the same four bulls. Some of each mixture was inseminated unfrozen (fresh semen) and another part after standard freezing at −196°C in