(b) The Supplementary type: when two unlike deter- 

 miners come together a modification occurs in the character; 

 seen in Castle's agouti guinea-pigs; 



In explanation of the results of experiments with guinea 

 pigs Castle postulates the action of a pattern factor in addi- 

 tion to the pigment factors (See Heredity in Coat Color in 

 Guinea pigs and Rabbits: Carn, Publ. 28. 1905). 



Problem. — Explain the following result: 9 agouti, 3 

 black, 4 white in the Fo generation when a black rabbit was 

 crossed with a white variety with factor for making the hair 

 yellow. 



(c) The Cumulative type: when two like determiners on 

 coming together effect the expression of character; observed 

 in Miss Durham's Intensified mice; 



Experiments were conducted upon mice of five types of 

 color, viz., albino, silver-fawn, chocolate, blue and black. In 

 explanation of the results it was found necessary to assume 

 the presence of an intensifying factor, or its absence a dilut- 

 ing factor, in addition to the pigment and color factors. 



(See Bateson, MendeVs Principles of Heredity, pp. SO- 

 BS). 



(d) The Inhibitory type: one determiner interfering 

 with the action of some other determiner. 



Examples of such inhibitor factors are found when the 

 Brown Leghorn is crossed with the Silky fowl, and when the 

 White Leghorn is crossed with the Brown Leghorn. 



(See Punnett, Mendelism). 



Problem. — Analyse and explain the following result: 

 13 white: 3 colored in F2 generation where a certain white 

 fowl is crossed with a certain colored fowl. 



In the White Leghorn the white behaves as a domin- 

 ant to color, but in the White Dorking and other white birds 

 white is recessive to color. When two such white birds are 

 crossed the results are as given below when the following 

 factors are assumed: 



C = Factor for color. 



c = Absence of factor for color. 



I = Inhibitor color factor. 



i = Absence of inhibitor factor. 



The White Leghorn will have the gametic formula of 

 CI. and the White Dorking ci. 



]07 



