Question

A test cross is carried out to confirm which of the following?

• A. The number of alleles present for all characters
• B. Whether the progeny is homozygous or heterozygous for the dominant trait
• C. Whether the recessive parent is homozygous or heterozygous for a respective trait
• D. To test whether the progeny acquired any genes from either parent

Answer 1

The correct option is B Whether the progeny is homozygous or heterozygous for the dominant trait

A test cross is a cross between a plant expressing dominant trait for a particular character with a plant expressing homozygous recessive trait for the same character.

Character is any visible feature of the organism and traits are variants of it. Diploid organisms have two copies of each trait.
Let us take for example, plant height as the character. Tallness (T) and dwarfness (t) would be the traits. T represents dominant copy, t represents the recessive copy. The dominant trait is able to express itself even if only one copy of it is available i.e., either TT or Tt will produce tall plants. Whereas the recessive trait is only able to express itself when identical copies of it are available, i.e., tt would be dwarf.

So, to find out whether the plant expressing the dominant trait is homozygous or heterozygous for the dominant trait, test cross is carried out.

In case of a test cross, one of the plants is known to be homozygous recessive.
There is no requirement for a test cross in case the progeny shows a recessive trait.
Recessive trait is expressed only in homozygous condition.

Number of alleles present for all characters cannot be determined from a test cross. Progeny obtained from crossing of two parental parents will definitely acquire genes from both the parents. So, a test cross will be of little use in this case.