Question

Test cross is a cross between

A. Hybrid $\times$ Dominant parent (Tt $\times$ TT)

B. Hybrid  $\times$ Recessive parent (Tt $\times$ tt)

C. Hybrid $\times$ Hybrid (Tt $\times$ Tt)

D. All the above

Answer 1

Hint: Back cross has two different types of cross, a test cross and outcross. Test cross (F1 generation and its recessive parent) and outcross (F1 generation and its dominant parent).

Step by step answer:
Test cross –
The Test cross is the cross that is done between the F1 generation and its pure recessive parent. It is the practice for tracing the genes of the parent.

Phenotypic Ratio – 2:2 or 1:1
Genotypic Ratio – 2:2 or 1:1
If the heterozygous parent is crossed with the recessive plant, then the F2 generation will have half tall and half short plants.

Phenotypic Ratio – Does not exist as all plants will be tall.
Genotypic Ratio – Does not exist as all plants have the same genotype.
If the homozygous dominant parent is crossed with the recessive plant, then the F2 generation will have all tall plants.
It is obvious that if the homozygous recessive parent is crossed with the recessive plant, then the F2 generation will have all dwarf plants.
Therefore, in the above way, the test cross helps to determine the genotype of the parents.
Thus, the test cross is the crossing between a plant and the recessive genotype.
Hence, option (B) is correct.
Additional Information: In genetics, whenever, an F1 generation is made to cross with its parental generation, then it is known as Back cross. Back cross is the crossing of the F1 generation with its parental generation. Since the parents can be of two types, Pure Dominant or Pure Recessive, the Back cross is of two kinds.
-Outcross
-Test cross

Outcross –
The outcross is the cross that is done between the F1 generation and its Pure dominant parent. It is the practice of introducing unrelated genetic material into the future generations. Outcrossing increases genetic diversity and reduces the probability of any organism to be subject to diseases or genetic abnormalities. It thus helps in reducing the inbreeding depression.

Phenotypic Ratio – Does not exist as all plants will be tall
Genotypic Ratio – 2:2 or 1:1

Note: There are two different crosses- test cross & Outcross. Even though both of these are kinds of the back cross, but they are different from one another. In a test cross, the F1 generation is exclusively crossed with the recessive parent only. The test cross helps in determining the genotype of the F1 generation. In the outcross, the crossing is done between the F1 generation and the dominant parent. It is done to increase genetic diversity.