202 OUTLINES OF EVOLUTIONARY BIOLOGY 



R G crossed with W Y gives the hybrid, R (G) (W) Y, which, owing 

 to the dominance of R and Y, will appear in the form of round 

 yellow seeds (the brackets around the G and W indicating the 

 recessive nature of green and wrinkled). That is not what our 

 gardener wants, and if he knew no better he would naturally be 



FIG. 80. An Example of Dihybridism in Peas. 



A, wrinkled yellow peas; B, round green peas; C, hybrid peas (Fi generation, round 

 and yellow in appearance) produced by crossing A and B; D, plant of the FI 

 generation, with seeds of the.F 2 generation, produced by self-fertilization and of the 

 four different kinds, round yellow, round green, wrinkled yellow, and wrinkled green, 

 lying in the pods. (Photographed from a preparation by Mr. Darbishire, who has 

 reproduced the same subject in colours in his work on " Breeding and the Mendeliaii 

 Discovery "). 



much disappointed with the result. If, however, the hybrids be 

 allowed to fertilize themselves and reproduce, then their off- 

 spring will appear in the apparent proportions : 



9 R Y : 3 R G : 3 W Y : 1 W G, 



no account being taken of the non-apparent recessive characters. 

 The meaning of the proportion 9:3:3:1 exhibited in this 



