274- 



PHYSIOLOGIC GENETICS 



Table 52 



Rank order of various breeds of cattle with regard to three hormone- 

 controlled PHYSIOLOGIC CHARACTERISTICS 



one criterion — body size. His foundation stock weighed about 23 grams, and, after 

 selecting for 21 generations, his small race weighed about 12 grams while the body 

 weight of the large race was 40 grams. Keeping in mind that the only criterion for 

 selection in this experiment was body weight, it is interesting to note that at about 

 the twelfth generation, the small race had a rate of ovulation of 7.2 eggs and a litter 

 size of 5.3 young, while the large race had a rate of ovulation of 14.1 eggs and a litter 

 size of 10.5 young. Although these data suggest that selection for one hormone- 

 controlled characteristic usually leads to an increase in the rate of secretion of other hor- 

 mones secreted by the same gland, data proving this by actual assay of glands or the 

 determination of hormonal levels are not readily available. 



In another study 46 ' 1066 a comparison was made of the hormonal contents of the 

 anterior pituitary glands of two strains of swine one of which was selected for a slow 

 rate of gain, the other for a rapid rate of gain. A comparison of the concentration of 



Table 53 



Comparison of the hormonal content of the adenohypophyses of two genetically 



different strains of swine 



Line selected 

 for 



No. of 



corpora 



lutea 



tis 



Testi 



No. of weight of 



embryos chicks (g.)f 



Body weight 

 of pigs 1 56 

 days old 



(kg.) 



Width of 

 epiphyses of 

 rats (micra) + 



Rapid growth 

 Slow growth 



14.5 

 10.5 



11.62 

 8.53 



15.7 

 25.2 



48.7 

 24.9 



243.4 ± 

 198.6 + 



15.6 

 8.1 



| Indicates gonadotrophic hormone content and 

 X content of growth hormone of adenohypophyses. 



gonadotrophic hormone and growth hormone in a standard quantity of pituitary 

 tissue was made at comparable ages in both strains (table 53). There was a significant 

 and clear-cut difference with regard to the concentration of growth hormone. Because 



