GENETICS 



v 



tors for genetical honors, until to-day it stands prob- 

 ably as the most famous experimental organism in the 

 whole world. 



Prof. T. H. Morgan of Columbia University is the 

 most conspicuous leader in the investigation of Droso- 

 phila. In his laboratory -over ten millions of these 

 animals, which literally "breed like flies," have passed in 

 review under the microscope while pedigrees of over 

 three hundred generations have been obtained and 

 recorded. In no other plant or animal has the remark- 

 able parallelism between the segregation of Mendelian 

 characters in experimental breeding and the behavior 

 of the chromosomes been so completely demonstrated. 



2. LINKAGE 



Drosophlla has only four pairs of chromosomes al- 

 though more than three hundred different characters 

 have been found in the flies themselves, a fact which 

 makes it at once evident that many genes, or character- 

 determiners, must be located together in each chromo- 

 some. 



Experimental breeding of Drosophila shows that 

 there is not always complete independent assortment of 

 the different characters that enter into a cross, as 

 Mendel found to be true for the different characters of 

 peas with which he experimented. 



Genes located together in any one chromosome are 

 likely to stay together during the conjugation of the 

 chromosomes and the subsequent separation of the 

 members of homologous pairs in the process of matura- 



