what is test cross?

What is back cross?

Back cross is the cross that involves the mating of the F1 hybrid with one of its parent. It can be explained with this example. Suppose a homozygous tall plant having genotype TT is crossed with the homozygous small plant having genotype tt, then their hybrid will be Tt (F1 plant). Now back cross is crossing this Tt individual with either TT or tt individual. 

Test cross is a cross in which an individual with an unknown dominant phenotype is crossed with an individual (parent) homozygous recessive for that trait.