Dihybrid Cross

 Dihybrid Cross: For conducting Dihybrid cross, Mendel selected 2 pairs of contrasting characters. Earlier Mendel took one pair of contrasting character for conducting his monohybrid experiment. For the dihybrid experiment, Mendel completed his experiment in the following way -

1st pair - Height             contrasting characters          Tall( TT )         and      Dwarf( tt )

2nd pair Seed shape        contrasting characters         Round( RR )    and      Wrinkle( rr )

For dihybrid experiment Mendel took dominant characters in one side and crossed it with the recessive characters in the following way-

                                       Tall Round     x    Dwarf Wrinkle

                                             TT RR                  tt rr

Ratio that he obtained from the dihybrid cross is 9:3:3:1

While doing this experiment Mendel formulated his another most important Law, "which is Law of  Independent Assortment".

Mendel found that the parental characters of Dihybrid experiment assort out independently in F2 generation.

That means -Tall Round(TT RR )  when crossed with Dwarf Wrinkle ( tt rr ) the F1 generation became Tall Round with the genotype (Tt Rr ), but in the F2 generation parental characters ie. TTRR and ttrr reappear.

Some Important Terminology:

Phenotype: Visible expression means can be seen, like tall or dwarf.

Genotype: Genetic constitution of individual, which cannot be seen. Like tall may be TT OR Tt. These  TT or Tt which are found through genetic study, known as Genotype.

Homozygous :      The organism carrying similar alleles for a trait, eg TT or tt.

Heterozygous :     The organism carrying different  alleles for a trait eg Tt

F1 Generation  :    The first Filial generation

Gametes         :    Reproductive unit, ( Sperm and Egg in case of human beings)

Dominant allele :   The parental character that occurs in the next generation.

Recessive allele:   The character which is unable to be expressed and remain suppressed is called Recessive allele