Question

Test cross determines:

• A. whether the traits remain unchanged when passed to the offspring
• B. the genotype of the individual under study
• C. the degree of successful breeding between two species
• D. number of alleles for a particular gene in the individual

Answer 1

The correct option is B the genotype of the individual under study

Test cross helps to predict the genotype of a dominant organism as it can be homozygous or heterozygous.

A test cross involves the cross between an organism showing the dominant phenotype for a particular character (whose genotype is to be assessed) with the recessive individual for the same character.

For example: the test cross conducted for a tall plant to determine the genotype (whether homozygous or heterozygous) is shown below.

Let T represent the allele responsible for tallness while t represent the allele responsible for dwarfness.

In order to determine the genotype of the tall plant, it is crossed with the dwarf plant.

If all the progeny obtained from the cross are tall plants, then the genotype is homozygous dominant (TT).

If tall and dwarf plants are obtained in the ratio of 1 : 1, then the genotype is heterozygous dominant (Tt).


However, test cross cannot determine whether the traits remain unchanged when passed to the offspring.

Successful breeding of the individuals of a species is determined by fertility of the individuals and also their genetic makeup.

The number of alleles for a gene cannot be determined by a test cross.