Question: 106. In a plant, black seed color ( \mathrm{BB} / \mathrm{Bb} ) is dominant over white seed color (bb). In order to find out the genotype of the black seed plant, with which of the following genotype will you cross it?
(1) BB
(2) bb
(3) Bb
(4) \mathrm{BB} / \mathrm{Bb}
Answer: Option (2)
Explanation:
When a dominant phenotype is observed, its genotype may be either homozygous dominant
\mathrm{BB} or heterozygous \mathrm{Bb}.
To determine the exact genotype of the black seed plant, a test cross is performed.
In a test cross, the individual with dominant phenotype is crossed with a homozygous recessive individual \mathrm{bb}.
If all progeny show black seed color, the genotype of the parent is \mathrm{BB}.
If both black and white seeded plants appear in the progeny, the genotype of the parent is \mathrm{Bb}.
Therefore, the black seed plant should be crossed with genotype \mathrm{bb}.