AN INTRODUCTION TO THE STUDY OF INHERITANCE 



In preceding studies attention has been called to the behavior 

 of the chromosomes in two kinds of mitosis. In one, somatic 

 mitosis, the chromosomes spUt equally as regards the quality 

 and quantity of materials which they comprise. Thus, two 

 daughter nuclei are formed exactly like each other and the result- 

 ing daughter cells are provided with the normal number of 

 chromosomes. In the other, reduction mitosis, the number of 

 chromosomes in the daughter nuclei through synapsis is reduced 

 by half. Such nuclei become those of the gametes. Thatjs, a 

 mature ovum and a mature spermatazoon each possesses*one- 

 half the number of chromosomes normal to the species. A 

 zygote (new individual) formed by the fusion of two such gametes 

 is not only provided with the normal number of chromosomes 

 but also half comes from each of the two parents. While the 

 offspring of a given pair of parents differ from one another in 

 certain details they nevertheless resemble each other more than 

 they resemble the individuals of any other group. This means 

 that there have been transmitted to the offspring the character- 

 potential of the parents which may become expressed and recog- 

 nized. In other words, the offspring biologically inherit from 

 two parents (biparental inheritance), each of which have inherited 

 from two parents, and so on back. It is, therefore, readily 

 understood that each individual harbors in its chromosomes a 

 great complex of heritable traits which may become expressed 

 according to chance combinations, thus accounting for both 

 similarities and differences which may be encountered among 

 the offspring. 



If heredity be interpreted as meaning "organic resemblance 

 based upon descent," no one can question its importance in the 

 study of the rise and perfection of animals. As one of the prin- 

 ciple methods of attack upon the problems of heredity is experi- 

 mental breeding, it has seemed advisable to introduce a study of a 

 simple Mendehan ratio. This study presupposes general famili- 

 arity with the subject gained from the textbook, assigned read- 

 ings, or lectures. 



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