The Making of Species 



we can see how it is that we get unilateral in- 

 heritance in the case of a cross. Where, however, 

 the units from the two parents intermingle, 

 although only one set is active in development, 

 the result will be blended inheritance. Thus, we 

 may regard the fertilised egg as made up of two 

 sets of characters a dominant set, which is active 

 in the production of the resulting organism, and 

 a recessive set, which appears to take little or no 

 part in the production of the organism. 



This is quite in accordance with Mendelian 

 conceptions. 



Let X be an organism having the unit char- 

 acters A B C D E F G, and let Y be another 

 organism having the unit characters a b c def g. 

 Now suppose that these behave as opposed 

 Mendelian units, and that the unit characters 

 in italics are dominant ones. Then the resulting 

 individual will resemble each parent in certain 

 unit characters. It may be represented by the 

 formula a B c d E f G, but it will contain the 

 characters AbCDeFg in a recessive form, 

 so that its complete formula may be written 



a Be dEf G\ 

 AbCDeFgj 



When these hybrids are paired together it will 



.,, , f ABCDEFG 



be possible to get such forms as A B C D E F G 



and a , l- i G r^ which exactly resemble the 

 a b c d e i g 



148 



