9. In test cross, F1 progeny is crossed with
(1) Either of the parent
(2) Recessive parent
(3) Dominant parent
(4) Heterozygous parent

Concept of a test cross

A test cross is used to determine whether an organism showing a dominant trait is homozygous dominant (AA) or heterozygous (Aa).
To do this reliably, it must be crossed with an individual that contributes only recessive alleles for the gene in question, i.e. a homozygous recessive (aa) parent. Any recessive phenotype among offspring proves that the tested individual carried the recessive allele (was Aa).

So in a test cross, the F₁ (or any unknown dominant) is crossed with the recessive parent.

Option-by-option explanation

1. Either of the parent

   • Wrong, because crossing with the dominant (homozygous) parent would give only dominant offspring and cannot distinguish AA from Aa. Only the recessive parent is informative.

2. Recessive parent – correct

   • The recessive parent is homozygous recessive (aa).

   • This ensures the genotype of the test organism is revealed by the offspring’s phenotypes:

     • All dominant offspring → tested parent is AA.

     • 1:1 dominant:recessive → tested parent is Aa.

3. Dominant parent

   • Crossing with a homozygous dominant (AA) will give all dominant offspring whether the test individual is AA or Aa. Genotype cannot be inferred; this is not a test cross.

4. Heterozygous parent

   • A heterozygous partner (Aa) produces a mixture of gametes that makes interpretation ambiguous; recessive offspring could arise in several genotype combinations. This is not the standard definition of a test cross.

Therefore, in a true test cross, the F₁ progeny (or any individual with a dominant phenotype and unknown genotype) is crossed with the homozygous recessive parent → option (2).