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 entities 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 destitute 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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