690 General and Applied Biology 



Parents (P) 

 Gametes produced 



Offspring (Fi) 



Gametes for both male and female 



DiHYBRiD Cross (Pea) (See Fig. 338) 



Round-yellow (RRYY) X Wrinkled-green (rryy) 



RY ry 



\ / 



\ / 



\ / 



\ / 



Round-yellow (RrYy) 



^ i i ^ 



RY Ry rY ry 



Offspring (Fz) when (Fi) are 



intercrossed or self-pollinated 

 (shown by the Punnet square) 



Male Gametes ^ 



From the above squares it is seen that the following offspring are secured; 



9 round-yellow 

 3 round-green 

 3 wrinkled-yellow 

 1 wrinkled-green 



This is the phenotype ratio 

 of 9-3-3-1 for a dihy- 

 brid cross in the F- gen- 

 eration. 



Parents (P) 



Gametes produced 

 Offspring (Fi) 



Trihybrid Cross (Pea) 



Tall-yellow-round X Dwarf-green-wrinkled 

 (TTYYRR) (ttyyrr) 



i i 



TYR tyr 



\ >/ 



Tall-yellow-round 



(TtYyRr) 



Gametes for both male and female TYR TYr TyR Tyr tYR tYr tyR tyr 



Offspring (Fo) by the Punnet square as in the monohybrid and dihybrid crosses, 

 there will be produced in the F2 generation the following: 



27 tall-yellow-round 



9 tall-green-round 



9 tall-yellow-wrinkled 



9 dwarf-yellow-round 



3 tall-green-wrinkled 



3 dwarf-green-round 



3 dwarf-yellow-wrinkled 



1 dwarf-green-wrinkled 



This is a typical F2 trihy- 

 brid, phenotype ratio of 

 27-9-9-9-3-3-3-1 when 

 such individuals as Fi 

 are used as parents. 



7. Incomplete Dominance. — From studies just made it was noted that 

 when opposite members of a pair of genes were present, one or the other 



