CHAPTER XII 



INTERMEDIATES 



So far as we have gone we have found it possible to 

 express the various characters of animals and plants in 

 terms of definite factors which are carried by the gametes, 

 and are distributed according to a definite scheme. 

 Whatever may be the nature of these factors it is possible 

 for purposes of analysis to treat them as indivisible en- 

 tities which may or may not be present in any given 

 gamete. When the factor is present it is present as a 

 whole. The visible properties developed by a zygote in the 

 course of its growth depend upon the nature and variety 

 of the factors carried in by the two gametes which went 

 to its making, and to a less degree upon whether each 

 factor was brought in by both gametes or by one only. 

 If the given factor is brought in by one gamete only, the 

 resulting heterozygote may be more or less intermediate 

 between the homozygous form with a double dose of the 

 factor and the homozygous form which is entirely des- 

 titute of the factor. Cases in point are those of the 

 primula flowers and the Andalusian fowls. Nevertheless 

 these intermediates produce only pure gametes, as is 



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