POPULATION GENETICS 



Study of the area are shown sHghtly simphfied in Figure 3. 

 The lesions produced by the French strain are distinctly 

 different from those of the Australian field strain and a com- 

 bined use of direct observations of the lesions in sick and 

 dead rabbits found in the area, with sub-inoculation in 

 doubtful cases, allowed a clear decision as to which strain 

 was responsible for each infection. It is clear that, although 

 an epizootic was initiated with the French strain, it faded 

 rapidly as soon as the epizootic due to the natural strain got 

 under way. 



Fig. 3. Selective advantage of Australian field strain A of myxomatosis 

 virus over the more lethal Fr strain. Simplified diagram showing daily- 

 findings of dead rabbits (ordinate) over period following liberation of the 

 virulent Fr strain. Total deaths and those due to A and Fr strains 

 separately are shown. 



These considerations of the processes of change in popula- 

 tions of bacteria and viruses were designed to act as an 

 introduction to the discussion of clonal selection amongst 

 the cells of the vertebrate organism, more specifically amongst 

 human mesenchymal cells. Throughout, a single theme has 

 been dominant — the potency of mutation and selective sur- 

 vival to change the character of a population of cells to bring 

 it into more appropriate relationship to its environment. 

 The remainder of these lectures are concerned to show that 

 this is as relevant to cell populations within the mammalian 

 body as to populations of viruses or bacteria. 



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