Menders Law 



45 



of their germinal constitution, arc said to be phciiotypi- 

 cally alike, or to belong to the same phoiolypc. On the 

 other hand, organisms having identical germinal con- 

 stitution are said to be genolypically alike, or to belong 

 to the same genotype. From the standpoint of pheno- 

 types only, Mendel's F2 generation shows the 3: i ratio; 

 but if genotypes are considered, it shows the 1:2:1 ratio. 



® ® 



Fig. 4. — Diagram illustrating behavior ot lirst generation (F,) 

 when inbred. Illustrates meaning of "segregation" and "purity of 

 gametes," and how chance matings of Fi gametes result in 3: i ratio in 

 F2 generation; dwarf individual produced only by zygote in lower right- 

 hand corner. 



In other words, this group of foniis contains two pheno- 

 types but three genotypes. J- 



Referring again to fig. 4, several things ma>' bet 

 inferred. It can be seen what will happen in the F, 

 generation when the F^ individuals arc inbred. The 

 dominant homozygote will ]:)roduce onl}- dominant 

 homozygotes in the F3 generation; the two hctcrozygotcs 

 will split up in the F3 generation in the same 1:2:1 ratio 

 as did their hybrid parents of the Fj generation; and 



