June, 1941] Animal Breedixg and Nutrition 5 



sic experiment with plants on which modern genetics is founded. If 

 this were so. animal breeding- would become a simple problem even 

 for the novice. This, howt'ver. has proven to be the exception in 

 animals. 



The object of experimentally applying genetic principles to the 

 breedirxg of livestock has thus been to design, if possible, what may 

 be termed genetic patterns of the probable gene complexes possess- 

 ed by parents for any given trait under consideration, in order to de- 

 termine from them (mathematically) the chance combinations of 

 such genes that will most probably occur in the offspring from a 

 cross in which parents differ. 



The practical application of such patterns is, however, limited to 

 the study of inheritance of body traits which are represented in the 

 germ plasm by a small number (2 or 3) genes. When the number of 

 genes required to produce a given trait (as appears to be the case 

 in most body characteristics pertaining to size) exceeds this, the pos- 

 sible combinations that may occur become so great as to lose signifi- 

 cance for a practical purpose. 



Crossing different breeds, or even species, for the production of 

 rew types is neither new nor unique, as most improved breeds of 

 livestock have originated by that method. The unique feature of 

 this experiment consists in the fact that this has l:»een a methodical 

 attempt to record measurements of about 60 different physical and 

 physiological traits of parentage and of the various generations of 

 their hybrid offspring as a basis for analyzing by statistical and 

 mathematical means the fimdamental laws that govern the transmis- 

 sion (i.e. the inheritance) of those traits. 



The data include records of live weight and of the measurements 

 of different parts of the body as representative of size and conforma- 

 tion ; also weight, market grade, and physical characteristics of the 

 wool ; the size and number of accessory nipples as indicative of milk 

 vield ; the frequency of twin offspring': and a numl)er of breed char- 

 acteristics which have no direct economic significance. 



During the time that this research has been in progress the birth 

 of about 2000 lambs has been recorded and frequent periodical rec- 

 ords have been obtained on all individuals. 



We have thus far found only a fe\v somatic traits : namely, horns, 

 color, ear length, and accessor\ nipples and milk yield which are sub- 

 ject to interpretation of a sufticiently simple gene complex to have 

 sigfnificance even for the trained breeder. 



We have so far mainly pointed out the complex eft'ect of the in- 

 heritance of type on function as a whole. How then does this help 

 the practical breeder of livestock who tries to maintain a high stand- 

 ard of type and function, or one who tries to improve on a low 

 standard? 



The result of these experiments has shown that an individual 

 which in itself represents a high standard of excellence of body or of 

 function may at the same time possess undesirable germinal quali- 

 fications. This is born out by the history of animal breeding opera- 

 tions over many years which shows that animals selected on basis 

 of their pedigrees or for their own individual physical merit have 



