Identify the correct statements about test cross.

(A). It can predict the genotype of the test organism
(B). It can distinguish homozygous and heterozygous among test organisms
(C). It is another name for back cross
(D). It is the law of dominance

Choose the correct answer from the options given below.

(A) and (B) only

The correct answer is Option (2) → (A) and (B) only 

Mendel crossed the tall plant from F2 with a dwarf plant. This he called a test cross. In a typical test cross an organism showing a dominant phenotype (and whose genotype is to be determined) is crossed with the recessive parent instead of self-crossing. The progenies of such a cross can easily be analysed to predict the genotype of the test organism.

In Test cross an organism showing a dominant phenotype (genotype unknown) is crossed with the recessive parent. In the case of dominant phenotype, by just looking at the morphology, it is difficult to find out whether the given plant is heterozygous or homozygous for dominance. In order to find the unknown genotype of the dominant character, a cross breeding is performed which is called test crossing. Here the unknown dominant character is crossed with the known recessive character, for example, tall plant (its genotype is not known) is crossed to dwarf (its genotype is known). In the cross, if the offsprings produced are of both dominant and recessive in equal ratio, the given plant is heterozygous for the said character. On the other hand, if the offsprings produced are all tall, then the tall plant is dominant homozygous. This type of crossing is employed to determine the heterozygosity or homozygosity of a suspected character.

If the dominant phenotype organism is homozygous dominant (e.g., AA), all offspring will show the dominant phenotype. If the dominant phenotype organism is heterozygous (e.g., Aa), the offspring will exhibit a 1:1 ratio of dominant to recessive phenotypes. This type of cross helps to reveal whether the dominant phenotype is due to a homozygous dominant or heterozygous genotype.

                                           Diagrammatic representation of a test cross