Section 14 — Animal Genetics and Breeding 



DNA of peking ducks was injected into a wild 

 duck. Under the influence of heterogenous des- 

 oxyribonucleic acid varied hereditary changes 

 appeared in subsequent generations in a small 

 percentage of cases. On this basis two dwarf 

 forms of snow-white ducks with lighthorn and 

 yellow beaks were obtained from a wild duck 

 treated with peking duck DNA. The variability 

 in ducks due to the effect of DNA injections was 

 only partially similar to the changes obtained in 

 cross transplantation of the testicle. 



14.26. Abnormal Segregations for the Alleles "single 

 Comb" and "Rose Comb" in the Domestic 

 Fowl. Ph. Me rat (Jouy-en-Josas, France). 



A study of the segregations of the alleles R 

 ("rose comb") and r ("single comb") in a poultry 

 population reveals the main following facts: 



(a) In the cross Rr x rr (with about 51.000 

 pedigree progeny) the male chicks show a 

 highly significant excess of single combs over 

 the rose combs; the proportion is normal by 

 the female progeny. 



(b) In the cross Rr x Rr (about 8000 pro- 

 geny), the female chicks show a highly significant 

 excess of single combs over the expected propor- 

 tion of 1/4; there is a deviation in the opposite 

 sense among the male chicks, so that, grouping 

 the two sexes, the ratio of the comb types is 

 normal, near 3/1. 



For these two crosses, the observed deviation 

 comes only from the progeny of some males. 



(c) For the cross rr x Rr (about 15,000 pro- 

 geny), on the whole, the ratio of the two comb 

 types is normal in both sexes. 



The hatching percentages, the sex ratio for 

 each comb type, and the different results ac- 

 cording to the type of cross, do not support 

 the hypothesis of a differential embryonic 

 mortality or of a differential fertility among the 

 ova. 



A progeny-test of single comb males from 

 "abnormal" families, the compared results in 

 the 3 crosses studied, and also in numerous 

 RR x rr crosses, do not lend support to the 

 hypothesis of modifying genes. 



The hypothesis of a selective fertilization 

 will be discussed. 



14.27. Effects of Selection on Reproductive Fitness 

 in the Fowl. A. W. Nordskog and Margrith 

 Wehrli (Ames, U.S.A.). 



Populations subjected to intensive artificial 

 selection for specific metric traits are expected 

 to decline in reproductive fitness. The latter is 

 defined here as a product of the components: 

 rate of egg production, fertility, hatchability, 

 and adult viability. Five lines starting from a 

 common Leghorn base population have each 

 been selected for a single trait over six genera- 

 tions. The breeding population of Line A, 

 selected for high egg production, consists of 

 16 sires each mated to 9-16 dams. Lines B and C 

 are selected for high and low body weight 

 respectively, and Lines D and E for high and 

 low egg weight, respectively. These lines are 

 maintained by 8 single-male pens of 9-16 dams 

 each. Line A has not improved consistently in 

 egg production or reproductive fitness. Body 

 weight has increased 54 per cent in Line B and 

 fitness has declined steadily by 47 per cent. Line 

 C has decreased 26 per cent in body weight; 

 fitness has declined 16 per cent. Egg size has 

 increased 15 percent in Line D, while fitness de- 

 creased 39 per cent. In Line E egg size has 

 decreased 14 per cent and fitness declined 16 

 per cent, but the latter is not statistically signi- 

 ficant. A similar selection experiment in the 

 Fayoumi breed shows good agreement. The 

 results fit the hypothesis that intermediate values 

 of body size genes are optimum to fitness. How- 

 ever, egg size in the original stocks appears to be 

 above the optimum for fitness such that down- 

 ward selection has either improved or maintained 

 reproductive fitness. 



14.28. Genetic Variation in Chick Bio-assays for 

 Gonadotropins. I. Testes Weight and Re- 

 sponse/ 1 ) P. B. Siegel and H. S. Siegel, 

 (Blacksburg, U.S.A.). 



Genetic influences on testes weights at hatch- 

 ing and testes weight response to anterior pitui- 

 tary homogenates and purified gonadotropins 

 were studied in White Rocks. Heritabilities were 

 estimated from paternal half-sib correlations. 

 Preparations were subcutaneously injected with 

 a saline carrier and responses measured as in- 

 crease in testes weight/100 g of body weight. 



Significant differences among sire families 

 were obtained from injections of anterior pitui- 

 tary homogenates. Responses among sire fami- 

 lies to 10 and 20 \xg. of FSH (Armour) were also 

 significantly different. The rank correlation of 

 family responses for the two dosages was 0.74 

 and the mean heritability of response was 0.92. 

 No significant differences among sire families 

 were noted for injections of either 100 or 200 \xg 



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