Section 9 — Population Genetics 



0.14 t 0.08, 9.34. 



weeks storage: x = 656.5 hr, hf 

 hf, = 0.63 ±0.12. 



The viability of embryos for 1 week of storage 

 was: x = 67.0 per cent, hf = 0.12 ± 0.03; 



2 weeks: x = 50.9 per cent, hj = 0.08 ± 0.03; 



3 weeks: x = 29.5 per cent, hf = 0.11 -_ 0.03. 

 Heritability was highest during the 0-7 day 

 incubation stage (hf = 0.08 to 0.16); the other 

 stage (8-29 day and pipping) had hf == 0.00 to 

 0.05. 



Developmental time was increased by storage 

 while viability decreased. Heritability estimates 

 were not materially changed for these traits by 

 the environmental changes. Developmental 

 time was influenced by maternal effects. Most of 

 the genetic variation of viability of turkey em- 

 bryos occurred during the 0-7- day stage of 

 incubation. 



9.33. The Effects of Temperature on Two Strains of 

 Mice of Different Body Weight and Tail 

 Length. F. Cockrem (Palmerston, New 

 Zealand). 



Two strains of mice, one of high body weight 

 and short tail length (line A), and one of low 

 body weight and long tail length (line B), have 

 been developed by selection. As an initial study 

 of possible correlated changes associated with 

 tail length and adaptive ability, the two lines 

 were reared at temperatures of 7°C, 21°C 

 (control) and 32°C from 3 weeks to 6 weeks of 

 age. Tail lengths and body weights were mea- 

 sured at these two ages. Ten males and 10 fe- 

 males of each strain were used for each treat- 

 ment. 



For both strains and sexes of mice, the cold 

 (but not the hot) treatment depressed body 

 weight growth. There were no interactions and 

 the effect of the treatments was proportional in 

 both strains of mice. For the variances of body 

 weight at 6 weeks, the only effect which was 

 consistent for both sexes was a reduction of 

 variance for the A line under the hot environ- 

 ment. 



For both lines a higher temperature was as- 

 sociated with a longer tail length, but line B show- 

 ed a greater increase under the hot and control 

 environment. Under the cold environment, both 

 lines showed a similar increase. 



Thus a genotypic difference in tail length was 

 associated with a difference in the degree of 

 response of this character to the three environ- 

 ments. Furthermore, a strain difference in tail 

 length and body weight was not associated with 

 a difference in the ability of the two strains to 

 adapt to the different temperatures. 



An Investigation of Genotype-environment 

 Interaction in the Mouse. Peter Hull (Roches- 

 ter, U.S.A.). 



It is to be expected that the genetic variance 

 between sires, estimated from the performance 

 of their progeny, will be small when the sires are 

 from the Fi of a cross between two highly inbred 

 lines, and larger when the sires are from the F2 

 of a cross of the same two inbred lines. From 

 previous work with poultry it was decided that 

 there was probably a relationship between the 

 magnitude of interaction of a group of genotypes 

 with environment, and the magnitude of the 

 additive genetic variance within the group of 

 genotypes tested. The results of the experiment 

 which is to be described are in agreement with 

 this hypothesis, since it was found that the inter- 

 action of sires with environment was greater 

 when the sires were from an F2 group than when 

 the sires were from an Fi group. This difference 

 was noted in the case of a metric character 

 (tail length), whose heritability was expected 

 to be comparatively high — in the case of a 

 second character (body weight), whose heritab- 

 ility might be expected to be lower, there was no 

 detectable difference in the size of the genotype- 

 environment interaction component of variance 

 between the two groups of sires. 



9.35. Selection Progress Toward an Absolute Limit 

 for Amount of White Hair on Mice. W. H. 



Kyle and H. D. Goodale (Lafayette and 

 Williamstown, U.S.A.). 



Selection for amount of white hair was ini- 

 tiated in 1931 by one of us (H.D.G.) in a stock 

 derived from one male mouse with a few white 

 hairs on its forehead and four self-colored fe- 

 males. A sample (5 males and 6 females) of the 

 selected stock was transferred to Purdue late in 

 1959 from which eight generations have been 

 produced. All mice were scored at weaning for 

 percentage of white on the dorsal surface. After 

 the first generation, numbers of offspring ranged 

 from 74 to 210. 



The unweighted mean per cent white of the 

 eight generations is 69.5 per cent for males and 

 64.7 per cent for females. Regression of sex 

 means on generations shows an average gain 

 per generation of 1.73 per cent for males and 

 0.55 per cent for females. Regressions of offspring 

 on parent are quite variable but indicate a low 

 degree of heritability. There is some indication 

 of a sex-linked effect. Standard deviations within 

 sex and generation are large. 



154 





