The genotype of a plant showing the dominant phenotype can be determined by
Back cross
Test cross
Dihybrid cross
Pedigree analysis
The correct option is Option 2) Test cross.
A test cross is a genetic cross between an individual showing the dominant phenotype (but with an unknown genotype) and an individual with the homozygous recessive genotype. The purpose of the test cross is to determine the genotype of the individual with the dominant phenotype.
By crossing the individual of unknown genotype with a known homozygous recessive individual, the phenotype of the offspring can reveal the genotype of the parent with the dominant phenotype. If the individual with the dominant phenotype is homozygous dominant (genotype AA), all the offspring in the test cross will show the dominant phenotype. However, if the individual with the dominant phenotype is heterozygous (genotype Aa), approximately half of the offspring will show the dominant phenotype, and the other half will show the recessive phenotype.