70 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



get as a result of algebraic multiplication the following possible combinations in 

 equal numbers: LL, Ls, Ls, ss. What will be the external appearance of the 

 flies containing each of these combinations? Will LL differ from Ls? Why? 

 What then will be the ratio of long- to short-winged individuals in the second 

 generation (Hegner, p. 289)? 



These experiments were first performed by a monk named Mendel, who 

 made crosses between different varieties of peas in the garden of the monastery 

 at Briinn, Austria. He discovered that in such crosses the differences between 

 the two plants that are crossed do not become permanently blended in the 

 offspring but separate out again unchanged in the second generation. This 

 behavior of the characters in crossing two different organisms is called Mendel's 

 law, and Mendel's results have since been confirmed on a very large number of 

 plants and animals. The conclusion which has been drawn from these experi- 

 ments is that the characteristics of animals are separate; that they are, so to 

 speak, independent units, which exist in some fashion or other as units in the 

 eggs and sperms; that these units remain separate in a hybrid organism even 

 though the hybrid may appear externally to be a blend of the characters of its 

 two unlike parents; and that under proper circumstances they may be made 

 to separate out again apparently unchanged. Modern research indicates that 

 the unit characters or, more correctly speaking, materials which represent the 

 unit characters are located in the chromatin of the nucleus. 



