Question

Differentiate between back cross and test cross.

Answer 1

Hint: The main difference between a test cross and a back cross lies in their role of action.

Complete answer: The major differences between the test cross and back cross are as follows:

Test cross	Back cross
Breeding of the dominant phenotype with the homozygous recessive phenotype (parent) is known as a test cross.	The breeding of F1 generation with one of its parent plants is known as a back cross.
All test crosses are backcrosses.	A backcross can be said as a test cross if the parent is recessive.
The F1 hybrid is crossed with a recessive genotype.	An F1 hybrid is crossed with either homozygous dominant or heterozygous genotypes.
The test cross helps in the identification of the genotype of the dominant individual.	The back cross helps in the identification of the elite genotype by checking the segregation of genes at the time of gamete formation.

Additional Information:
1. Zygosity refers to the proportion of individuals that can be either homozygous or heterozygous. A heterozygous genotype has a dominant and a recessive allele. Whereas a homozygous genotype can have either both dominant or both recessive alleles.
2. If in a test cross, the dominant character (F1) is heterozygous, then crossing it with a recessive parent will also produce a recessive product whereas if the dominant character (F1) is homozygous then it will not produce any recessive product.

Note:
1. In animals, the back cross is also referred to as a ‘top cross'.
2. The back cross and test cross were first discovered by Gregor Mendel during his hybridization experiment on the pea plant.
3. All the crosses can be diagrammatically presented with the help of a square known as Punnett square. Let us understand the test cross with the help of a Punnett square.