Question

In the F₂ generation of a cross, progeny having different traits are produced in the ratio 3:1. State whether it is a monohybrid cross or a dihybrid cross. Give one example of such a cross.

Answer 1

This is an example of monohybrid cross. In this type of cross, the phenotypic ratio is obatined as 3:1 whereas the genotypic ration is obtained 1:2:1.

Example: A cross between true breeding tall (TT) and true breeding dwarf (tt) plants.

In this cross, all the F₁ progeny produced would be tall (Tt) since the allele for tallness is dominant over the allele for dwarfness. When the F₁ generation is selfed, the F₂ generation so produced contains both tall and dwarf plants in the ratio 1 : 2 : 1. The cross involved is as follows:

The phenotypic ratio is 3:1 i.e. 3 tall plants and 1 dwarf plant.