Mendel's Law 39 



typically and phenotypically, that is, with the same 

 germinal constitution and the same appearance. By in- 

 . breeding these Fi individuals, it will be seen that four 

 kinds of gametes are involved. Crossing these four kinds 

 of gametes the resulting combinations are indicated in 

 fig. 5. The result is four phenotypes, as follows: nos. i, 2, 

 3i 4> Si 7) 9) 10, 13 are tall smooth individuals; 11, 12, 

 15 are dwarf smooth; nos. 6, 8, 14 are tall wrinkled; 

 no. 16 is dwarf wrinkled. This is the 9:3:3:1 ratio. 



It will be noticed that nos. i, 6, 11, 16 are homo- 

 zygotes and therefore will breed true; but the rest are 

 heterozygotes, either for one pair of characters or for 

 both, and these would split into various types upon 

 further breeding. 



The next step is the trihybrid ratio. Mendel found 

 yellow seeds dominant over green seeds, and if this pair 

 of characters is included with those used above the tri- 

 hybrid result can be observed. The experiment would 

 consist in crossing tall, smooth, yellow individuals 

 with dwarf, wrinkled, green individuals; and it is 

 obvious that the hybrid progeny would all be tall, 

 smooth, yellow, since these three characters are domi- 

 nant. Inbreeding the hybrids gives the following 

 result in the Fj generation: 27 tall smooth yellow, 9 tall 

 smooth green, 9 tall wrinkled yellow, 9 dwarf smooth 

 yellowj 3 tall wrinkled green, 3 dwarf smooth green, 

 3 dwarf wrinkled yellow, i dwarf wrinkled green. 

 The trihybrid ratio therefore is 27:9:9:9:3:3:3:1. 

 This involves 64 individuals and 8 phenotypes. 



1. JoHANNSEN, W., Elemente der exakten Erblichkeitslehre. 

 Jena. 1909. 



2. Mendel, G., Versuche iiber Pflanzen-Hybriden. Verb. Naturf . 

 Vereins in Briinn 4: 1865. 



