Section 14 — Animal Genetics and Breeding 



lymphocytes to 30 per cent granulocytes 5. 

 A polygenic type of inheritance is hypothe- 

 sized with not less than four, and possibly more, 

 pairs of factors. 



14.9. Adrenocortical Variation in Mus nwscuius. 

 F. M. Badr and S. G. Spickett (Cambridge, 

 Great Britain). 



Study of the adrenal cortex of the house mouse 

 reveals wide variation in the ratio of adrenal 

 weight to body weight both between long stand- 

 ing inbred strains and between laboratory bred 

 wild strains. This variation is, in part, the ex- 

 pression of variation in adreno-cortical zona- 

 tion. Different strains show variation in the levels 

 of circulating corticosteroids and in the levels 

 of excreted steroid metabolites. This is due to 

 variation in adrenocortical synthetic activity 

 as determined by in vitro incubation, and in the 

 A 4 hydrogenase activity of the liver, and adrenal 

 cortex. 



Studies of hybrids indicates that this variation 

 is, in large measure, of genetic origin. 



14.10. Genetic Studies on the Resistance of Polyoma 

 induced Mouse Tumour Cells to Polyoma 

 Virus Infection. David Gershon and Leo 

 Sachs (Rehovoth, Israel). 



Resistance to challenge infection with poly- 

 oma virus (PV) was studied in 88 tissue culture 

 clones from PV induced mouse tumors, to de- 

 termine whether there exists in these mammalian 

 cells any similarity to the immunity to superin- 

 fection found in lysogenic bacteria. There 

 was no spontaneous virus production by any 

 of these clones. Cloning of two resistant un- 

 cloned mass populations yielded about 50 per 

 cent susceptible clones, while cloning of two 

 susceptible clones yielded 7 and 37 per cent 

 resistant clones. A segregation of resistant from 

 susceptible clones was observed through two 

 cycles of recloning. Although the resistant unclon- 

 ed populations segregated susceptible clones in the 

 first cloning cycle, second cycle cloning of resistant 

 clones yielded only resistant clones. In contrast 

 to lysogenic bacteria, susceptible cells thus 

 segregated back to resistance in the absence 

 of new virus infection. Treatment of two resis- 

 tant clones with acridine orange did not render 

 them susceptible. Both resistant and susceptible 

 clones produced tumors in mice, and possessed 

 the PV induced cell antigen. There was no ap- 

 parent correlation between differences in the 



chromosome number of the tumor cells and their 

 response to challenge infection. The results will 

 be discussed in relation to the possible me- 

 chanisms that determine resistance and suscep- 

 tibility of PV induced tumor cells to PV chal- 

 lenge infection. 



14.11. Selection and a Maternal Effect. Nigel 

 Bateman (Edinburgh, Great Britain). 



Individual, family and within-family selections 

 are often regarded as alternative methods, merely 

 differing in efficiency, for selecting the same 

 genes for improving the genotypes of indi- 

 viduals. The possibility that family selection 

 especially, and to a lesser extent individual 

 selection, could give qualitatively different 

 results from within-family selection by procuring 

 heritable maternal effects semes to have been 

 mostly overlooked. The importance of such 

 effects for 5-week weight in the mouse is de- 

 scribed. 



Both sexes were selected on individual 5-week 

 weight. After ten generations heavy mice weighed 

 34 g and light mice weighed 17 g. Their difference 

 amounted to 32 per cent of the accumulated 

 selection differential. Differences between off- 

 spring of the worst individuals and the selected 

 lines averaged 39 per cent of selection. Presuma- 

 bly on account of maternal effects, reciprocal 

 hybrids differed by 43 per cent of the weight 

 difference between parental lines. The responses 

 of the selected lines and of offspring of the 

 worst individuals could be accounted for if 

 one-quarter of the maternal effect stemmed from 

 maternal 5-week weight and maternal genotype 

 (selected through family differences which con- 

 stituted two-thirds of the superiority of selected 

 individuals) determined the remainder. 



At the beginning of the experiment a simple 

 1: 2: 3 relationship obtained between weights 

 at 3, 5 and 9 weeks of age. Unexpectedly, the 

 selection on 5-week weight alone left this 

 relationship unchanged in both selected lines 

 though the hybrids did not conform. In fact, 

 the inherent growth curves for the selected lines 

 had changed, but were masked by changes in 

 the maternal effects. 



14.12. The Spermatozoa of Mouse-Strains selected 

 for Body Weight. R. A. Beatty (Edinburgh, 

 Great Britain). 



When n strains of mice are crossed in all 

 possible ways, the n 2 types of progeny fall into 



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