NEED OF EXPERIMENTAL STUDY 537 



Active and Latent Genes. Not all of the genes inherited 

 manifest themselves, for many lie dormant and consequently 

 cause no corresponding characters to develop. Sometimes they 

 lie dormant for a generation or more and then become active. 

 On this account offspring may have ancestral characters which 

 the parents did not have. Certain genes for male characters 

 are always latent in females. Thus a mother may transmit to 

 her son genes for a beard like her father's, although she develops 

 no beard herself. It is obvious that one cannot accurately judge 

 the constitution of a plant or animal by the characters present, 

 for judgment based upon external appearances takes no account 

 of the latent genes. Further breeding is necessary to determine 

 these. Latent genes becoming active is, therefore, one of bhe 

 reasons why offspring differ from their parents. 



Importance of the Study of Heredity. The study of her- 

 edity occupies an important position among the sciences. The 

 study of heredity has for its aim the discovery of the laws of 

 heredity, and a knowledge of these laws is essential in many 

 lines of work. The improvement of our crop plants and domes- 

 tic animals through breeding depends upon the laws of heredity. 

 The science of sociology and all sciences dealing with the physical, 

 moral, and spiritual welfare of humanity are moTre or less con- 

 cerned with the laws of heredity. Even in the realm of medi- 

 cine the laws of heredity are taken into account. 



Experimental Study of Heredity 



Need of Experimental Study. In the discussion of evolution 

 it was shown that the application of the experimental method 

 to the study of evolution has added much to our knowledge 

 of this subject. We had no definite knowledge of the kinds of 

 variations and their relation to natural selection until they 

 were studied by the experimental method. In the study of 

 heredity the experimental method is as essential as in the study 

 of evolution. Heredity is so apparent in both plants and ani- 

 mals that we are all convinced of its reality. That children 

 resemble their parents in habits, disposition, color of eyes and 

 hair, and other features is so noticeable as to be a matter 

 of common observation. Casual observations, however, fall 

 short of giving us a knowledge of the] laws of heredity. The 



