DIHYBRID GENETIC CROSSES

Class Notes Review

 

        Solving Dihybrid genetic problems is not difficult, but it does take time!  Follow these steps in order to solve any dihybrid problem.

 

                        1.    Set up a chart with all the phenotypes and genotypes.

                                Example:           Phenotype                                        Genotypes

                                (Trait 1)               Tall                                                TT, Tt

                                                             Short                                              tt

 

                                (Trait 2)                Red                                                RR, Rr

                                                             White                                              rr

 

                    2.        Determine the Parent (P) genotypes.

                                Parents are Homozygous Dominant and Homozygous Recessive

                                                           TTRR                    and              ttrr

 

                    3.        Using the F O I L method set up the Punnett Square for four allele combinations.

                                    (FOIL = First, Outer, Inner, Last)

 

 

F1 TR TR TR TR
tr TtRr TtRr TtRr TtRr
tr TtRr TtRr TtRr TtRr
tr TtRr TtRr TtRr TtRr
tr TtRr TtRr TtRr TtRr

 

                       

                           4.            Determine Genotypic and Phenotypic Ratio

                                                F1 genotype  is 100%  TtRr  (hybrid)

                                                F1 phenotype is 100% Tall and Red