Linkage 



103 



cent Tr; 5 per cent tR; or 9 TR, 9 Ir, i 7>, i IR. 'J1ie F^ 

 population which results from the random matings among 

 this assortment of gametes is represented in fig. 19, the 

 phenotypic ratio being 281 tall red: 19 tall white: 19 



R R 



81 



^T) Cl 



R 



fT\ 



R 



rT\ 



R 



R 



R 



T 



R 



81 



vly 



^f t 



R Ji^ 

 9 9 



^^T7^ 



R 



R R 



R 



II 



12 



R 



t 



R 



t t 



tut 



13 



14 



16 



• Fig. 19. — Showing F2 population produced by random mating of 

 gametes of Fi in a case of linkage with 10 per cent crossing over. 



dwarf red: 81 dwarf w^hite. In such cases, of course, the 

 original investigator has for his data only this final pheno- 

 typic ratio, and from these data must compute the 

 amount of crossing over that has taken place. In actual 

 practice this computation would be simplified by the 

 use of a formula. As a matter of fact, the necessity of 



