THE BIOMETRICAL ANALYSIS 



genetics extends mendelism to all, or nearly all, variation. In making 

 this extension we learn to measure variation by new quantities and 

 to understand it in terms of new units: quantities and units as 

 appropriate to the study of continuous variation as the segregation 

 ratios, recombination frequencies and individual genes are to the 

 study of discontinuous variation. 



The mcndelian foundation upon which the biometrical method 

 rests has been laid by the study of major differences. The geneticist 

 has chosen the variants which he needed for this purpose from 

 amongst the wealth of variation which living species offer him. He 

 has not been concerned with the phenotype except in so far as its 

 changes and differences marked for him changes and differences 

 of the genotype whose understanding was his primary aim. No 

 such choice is open to the breeder of crops and stock. His aim must 

 always be to adjust and improve the performance of his plants and 

 animals in respect of some character, yield, quality, disease resistance 

 or whatever it may be, which is chosen for him. He must be pre- 

 pared to make good use of whatever heritable variation, continuous 

 or discontinuous, his individuals may show. It is for this purpose 

 that he, no less than the student of ultimate principles, needs the 

 integration of the mendelian and biometrical techniques which we 

 can now attain. 



REFERENCES 



nsHER, R. A. 1918. The correlation between relatives on the supposition of mcn- 

 delian inheritance. Trans. Roy. Soc. Eiiin., 52: 399-433. 



nsHER, R. A., IMMER, F. R., and TEDIN, o. 1932. Thc genetical interpretation of 

 statistics of the tliird degree in the study of quantitative inheritance. Genetics, 

 17: 107-124. 



MATHER, K. 1949. BiowetricaJ Genetics. London. 



PANSE, V. G. 1940. The application of genetics to plant breeding. II. The inheritance 

 of quantitative characters and plant breeding. _/. Genet., 40: 2S3-302. 



94 



