INHERITANCE— IMP RO VEMENT B V BREEDING 1 8 7 



It is conceivable that there might be other interactions of chap 

 factors in a trihybrid combination of this character, which would v - 

 give quite different Mendelian ratios ; for instance if A were 

 only visible in the presence of C we should have a ratio of — 



36 AC: 21 B:3 A: 3 C : 1 abc 



of which A and C might conceivably give the same appear- 

 ance as abc, giving an apparent ratio of 36 : 2 1 : 7. 



Bateson gives the following scheme by which the number 

 of types, and the ratios in which each will appear, is given for 

 any number of pairs of factors, one factor of each pair being 

 dominant and the other recessive. 



4 = 3 + 1 



16 = (3 + r) 2 = 3" + 3 + 3 + 1 = 9 + 3 + 3 + I 

 64 = (3 + i) :l = 3 :l + 3'3 2 + 3'3 + 1 = 27 + 27 + 9 + 1 

 256 = (3 + i)* = 3 4 + 4 -3 :) + 6-3= + 4-3 + 1 

 = Si + 27 + 27 + 27 + 27 



+9+9+9+9+9+9 



+3+3+3+3 

 + 1. 



So in general 



4" = 3" 



+ 3"" 1 + 3""" 1 + " times 



+ 3"~ J + 3"~ 2 + i" (" ~ x ) times 



+ 3"~ ;1 + 3"~ :1 + J« (h - 1) (11 - 2) times. 



+ etc. 



140. Inheritance of Colour. — There are several different 

 colours in the maize grain, and also in the vegetative part of 

 the growing plant, which behave as separate allelomorphic 

 pairs, transmissible independently. In a few cases coupling 

 of allelomorphs appears to take place. Owing to the different 

 behaviour of these several colours it will be convenient to dis- 

 cuss them separately. 



141. Yellow Endosperm. — Yellow colour of the endosperm 

 and its absence behave as an allelomorphic pair. 



Shull, East and Hayes, and the present writer have found 

 two kinds of yellow each of which behaves with its opposite as 

 an independent allelomorphic pair. One of these (the darker 

 yellow) gives the Mendelian ratio 1 : 2 : 1 ; the other (the 

 paler) gives the ratio 9:3:3:1. In some cases the latter is 

 so faint as to be easily overlooked in a poor light, and has been 

 mistaken for a "dominant white". If non-yellows breed true 



