iS 4 



MAIZE 



CHAP. 

 V. 



When this ratio is met with in a heterozygous family, we 

 conclude that we are dealing with a dihybrid. 



The following example of a dihybrid cross (ear 1,157) 

 between a white wrinkled and a red starchy maize is taken at 

 random from among the writer's records : — 



Table XXXIV. 



ANALYSIS OF A DIHYBRID CROSS BETWEEN WHITE WRINKLED 

 AND RED STARCHY MAIZE. 



139. Trihybrid Ratios. — Crosses are met with in which a 

 third factor, which we may designate as C, has an influence on 

 the second factor B, so that when the two meet they produce 

 colour, but when either is absent, the appearance is the same 

 as though neither was present. In such cases we get the 

 ratio 48 : 9 : 7. By growing on the seven recessives we find 

 that they are not homozygous, but consist of 3 B, 3 C and 

 1 abc, the latter only (i.e. i z of all) a pure recessive ; the 

 actual ratio is therefore : — 



48 : g : 6 : 1 

 or 



75 : 1.4-0625 : 9-375 : 1-5625 per cent. 



When three allelomorphic pairs (e.g. Aa.'Bb, and Cc) enter 

 into the cross, there are sixty-four possible combinations of 

 these characters. In such a cross the results will be : — 



