Test Cross

Cross of F1 dominant offspring with its homozygous recessive parent is called a Test cross.

• Used to determine genotype of F₁ offspring, whether it is homozygous or heterozygous.
• OR, we can say, Cross of an organism with dominant phenotype (and whose genotype is to be determined) is crossed with the homozygous recessive parent. The outcome of the testcross can reveal the unknown genotype.
• Like, cross of F₁ tall pea plant with tt parental phenotype.
• F₁ plant could be either homozygous (TT) or heterozygous (Tt), because tallness is a dominant trait in peas.
• We can determine its genotype by performing a testcross.
• Testcross would produce all tall progeny (all Tt), if the plant is homozygous (TT).

Test Cross(if F1 is homozygous)

• Testcross would produce half tall progeny and half dwarf progeny (Tt,Tt,  tt and tt), if the plant is heterozygous (Tt), 

Test Cross (if F1 plant is Heterozygous)

• In a testcross, any recessive allele in the unknown genotype is expressed in the progeny, because get paired with a recessive allele from the homozygous recessive parent.

Back cross

• Cross of F1 offspring with any of the parental genotypes (homozygous dominant or homozygous recessive) is called a
• Test cross is a type of backcross.