Back cross and test cross definition

Difference between test cross and back cross

The Main difference between test cross and back cross is that Test cross is the cross that occurs between a dominant phenotype and a recessive phenotype, while backcross is the cross that occurs between the generation F1 hybrid and either parent.

Understanding the difference between test cross and back cross is important in genetics as they are two different types of cross that are extremely helpful in identifying the genotype of an animal or plant. The main goal of performing the test cross and back cross is to detect heterozygosity or homozygosity of individuals by identifying the types of gametes that produce the dominant genotypes.

Consider the following example to understand both crosses and the difference between test cross and backcross. Here "T" denotes the dominant trait of the tall pea plant and "t" denotes the recessive trait of the same phenotype. A large pea plant hybrid can be either homozygous (TT) or heterozygous (Tt), and the dwarf plant hybrid is always homozygous recessive (tt).

1. Overview and main difference
2. What is Test Cross?
3. What is backcross?
4. Similarities between test cross and back cross
5. Side by side comparison - test cross versus back cross in tabular form
6. Summary

What is Test Cross?

In the test cross, the 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 take the test cross to determine whether an individual is heterozygous or homozygous for the dominant character. In addition to discovering heterozygosity, the test cross is also useful for checking the purity of the gametes produced by the parents.

When a homozygous dominant F1 hybrid (TT) crosses with the recessive parent, it always results in 100% heterozygous large hybrids. The following figure explains this.

When a heterozygous F1 dominant hybrid (Tt) crosses with the recessive parent, only 50% are tall and the remaining 50% are dwarfs. The following picture explains this.

What is backcross?

In backcrossing, the F1 hybrid is crossed with one of the parents, either dominant or recessive. Backcrossing increases the beneficial traits in a population. For example, certain crop hybrids are backcrossed with wild species to restore their beneficial traits such as disease resistance, high yield, and so on.

However, this process can dilute the other beneficial traits of hybrid. To overcome this disadvantage, hybrids are repeatedly crossed back with their parent plants over a number of generations in order to transfer their good traits back into the new hybrids.

What are the Similarities Between Test Cross and Backcross?

  • Test crossbreeding and backcrossing are useful in plant and animal breeding.
  • They explain the phenotypes and genotypes of an organism and how they are passed on to the next generation.
  • All test crosses are backcrosses.
  • They determine an individual's genotype and help restore important traits.
  • In both cases the cross is between unknown genotypes.

What is the difference between test cross and backcross?

Test cross and back cross are two types of popular crosses in plant breeding. The test cross is between a dominant phenotype and the recessive phenotype in order to determine the genotype of the dominant phenotype. Backcross helps restore important traits of the parent population in hybrid populations.

Summary - Test Cross vs Backcross

All test crosses are some kind of backcross, but all backcrosses are not test crosses. During backcrossing, the F1 hybrid is backcrossed with one of the parents, either homozygous or heterozygous. During the test crossing, however, the F1 hybrid is always backcrossed with the recessive parent. Test crossbreeding is important to determine the genotype (TT or Tt) of the dominant phenotype, while backcrossing is useful in restoring important traits in the parent. This is the difference between a test cross and a back cross.