03 Inheritance and Variation - part 04 - Back Cross and Test Cross

03 Inheritance and Variation - part 04 - Back Cross and Test Cross


Back Cross and Test Cross : 

a. Back cross : 
  • The F1 individuals obtained in a cross are usually selfed to get the F2 progeny. 
  • They can also be crossed with one of the two parents from which they were derived (either recessive or dominant). Such a cross is known as back cross. 
b. Test cross : 
  • The cross of F1 hybrid with the homozygous recessive parent is known as a test cross. 
  • Used to test whether an individual is homozygous (pure) or heterozygous(hybrid). 
  • It is easy, simple, repeatable and predictable. 
  • Used to find out genotype of any plant with dominant expression. But it is not known whether it is homozygous (pure) or heterozygous for that trait. 
  • For example, A pea plant having violet (purple) flowers is crossed with a pea plant with white flowers.  If all flowers produced are violet, we can conclude that plant is pure or homozygous and if we get violet and white flowers in 1:1ratio.we can conclude that plant is heterozygous. 
  • Used to introduce useful recessive traits in the hybrids of self pollinated plants during rapid crop improvement programs. 
  • Recessive parent is crossed to find out unknown genotype.

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