MUTATIONS IN PLANT BRELDING afd 
of the seedlings exhibiting the new characters. In cross-fertilized species, 
in which individual plants are self-sterile, where a mutation appears 
in only one plant, several successive crosses may be necessary in order 
to produce a strain which breeds true for the new type. It must be 
crossed back on the parental form to begin with. If the change from 
the parental type is conditioned by a single factor the number of hybrid 
generations to be raised will depend on whether that factor segregates as a 
dominant or a recessive. In the latter case a true breeding strain should 
be obtained in the second generation but in the former it will require 
three or more hybrid generations depending on the extent to which the 
new characters depend upon environmental conditions for their expression. 
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