In test cross, F1 hybrid is crossed back with the recessive parent. In other words, test cross is the cross between a dominant phenotype (TT or Tt) and a homozygous recessive (tt). Mendel was the first person to perform the test cross to identify whether an individual is heterozygous or homozygous for dominant character. Other than discovering heterozygosity, test cross is also useful to check the purity of the gametes produced by parents.

If homozygous dominant F1 hybrid (TT) is crossed with the recessive parent, it will always result receive 100 percent heterozygous tall hybrids.

If heterozygous dominant F1 hybrid (Tt) is test crossed with the recessive parent, only 50% will be tall and the rest 50% will be dwarf.

In backcross, F1 hybrid is crossed back with any of the parent, either dominant or recessive. Back crosses are used to increase useful traits in a population. For example, certain crop plant hybrids are backcrossed with wild species to obtain its useful traits such as disease resistance. However, this process may dilute the other useful traits of hybrid. In order to overcome this disadvantage, hybrids are backcrossed repeatedly with its parent plants over few generations to receive their good traits back into the new hybrids.

Difference between Test Cross and Backcross

• All test crosses are considered as backcrosses, but all backcrosses are not the test crosses.

• During backcross, F1 hybrid is crossed back with any of the parents, either homozygous or heterozygous. However, during test cross, F 1 hybrid is always crossed back with the recessive parent.