CHAPTER V 

 INDEPENDENT MENDELIAN INHERITANCE 



Essentially Mendelism is an attempt to explain the result of heredity 

 on a rigid, statistical basis. Morgan has stated that the cardinal feature 

 of Mendelism is the fact that when the hybrid forms germ cells the 

 factors segregate from each other without having been contaminated one 

 by the other. The presence or absence of any contamination of factors 

 is still a debatable subject as will be apparent from later discussions, but 

 for all practical purposes the absence of such contamination may be re- 

 garded as an established fact. The other implications of this statement 

 that the two germ-cells which unite to produce the individual each con- 

 tribute an homologous set of hereditary units or factors which determine 

 the characters of the individual and that these units again separate from 

 each other in germ-cell formation are the fundamental conceptions of 

 Mendelism. When the units are considered pair by pair one member of 

 each of which has been derived from each parent, it is clear that the im- 

 portant feature of Mendel's discovery lies in the segregation of the 

 members of each pair in germ-cell formation. 



The statistical laws of segregation of characters were first announced 

 by Johann Gregor Mendel, Augustinian monk and later Pralat of the 

 Konigskloster at Briinn, Austria. In 1865 after 8 years of thorough 

 and painstaking research which is even today a model of genetic inves- 

 tigation, he read the results of his investigations before a meeting of a 

 local scientific society, the Natural History Society of Briinn, and the 

 following year the paper was published in the transactions of this society. 

 Unfortunately, however, the announcement of the work was made at a 

 time when the scientific world was not in a position to appreciate its 

 full significance and was busy with other things. The results, therefore, 

 were neglected until in 1900, the independent investigations by the 

 three botanists, Correns, von Tschermak, and de Vries, led to similar 

 conclusions and to the rediscovery, of Mendel's paper. By that time 

 experimental research had so far advanced that the importance of Mendel's 

 work was immediately recognized and it was not long before a vast 

 series of investigations had been reported in confirmation of it. 



The Monohybrid. The operation of Mendelism is best followed by 

 considering an actual experiment. Mendel crossed tall and dwarf peas 

 and obtained hybrid plants, all of which were tall like the tall parent. 



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