Reflexion of Genetic Differences by Spermatozoan Antigens

INDIVIDUAL rams of one breed differ in both spermatozoan and seminal plasma antigens¹ and breeds of ram show similar differences (A. C. K., unpublished). We have examined spermatozoan antigens in rabbits of different genotype at the albino locus, using the Edinburgh AS stock. This uniform stock has been bred for some 20 yr without grandparents in common so as to avoid formation of sublines. In each generation, mating between heterozygotes yields homozygous albino (cc); the heterozygote, or “light sable”, (cc^chL) and homozygous light chinchilla, or “dark sable” (c^cHLc^chL), in numbers close to the 1:2:1 Mendelian expectation. Although numerous genes will be segregating, the repeated crossing over will have ensured that the only constant genetic difference between the three types of rabbit will be at or close to the albino locus.     

Effects of social conditions on Juvenile Hormone mediated reproductive development in Bombus terrestris workers

Abstract. During the annual life cycle of the bumble bee Bombus terrestris (L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) release in vitro , ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.     

Cytological Studies in the Cycads: Sex Chromosomes in Cycas

The chromosomes of Cycas pectinata are studied from root tipand pollen mitoses. The male and female plants showed the samenumber of chromosomes (2n = 22) with almost identical chromosomemorphology. The only difference is that in the female planttwo chromosomes of the somatic complement (pair III) bear satellites,while in the male the same pair is heteromorphic with only oneof its members bearing a satellite. This becomes further clearwhen two types of haplid complements are noticed in pollen mitosis,one type possessing a satellited chromosome, and the other showingnone bearing a satellite. The pair of chromosomes which is heteromorphic in the male isassumed to be associated with sex determination in Cycas, themale being the heterogametic sex with XY type of sex chromosomes.     

The Effect of Annual and Bi-annual Pruning on the Seasonal Changes in Xylem Formation in the Grapevine: With five Figures in the Text

Growth-ring development and seasonal changes in starch contentwere examined in annually as well as bi-annually pruned grapevines.Cambium was generally found to be active (in its normal season)from the middle of April to the end of July, with the main periodof activity being May to June. As a result of an additionalpruning in August a second period of cambial activity beganin the middle of September and lasted until the middle of November,with the main activity occurring in October. In the ‘normal’early summer season cambial activity was found to expand fromthe canes in a basipetal direction, whereas in the late summerseason it recommenced simultaneously in the trunks and canes.In vines that had been pruned twice in the preceding year theearly summer xylem increment was smaller than in those whichhad been pruned only once and the total increment of two growth-ringsper year was similar to that of the one growth-ring in the latter,once pruned, plants.