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The genotype of a plant showing the dominant phenotype can be determined by
A
Back cross
B
Test cross
C
Dihybrid cross
D
Pedigree analysis
Detailed Solution
A plant with the dominant phenotype may be homozygous (TT) or heterozygous (Tt); the two cannot be told apart by appearance.
In a test cross the plant is crossed with the homozygous recessive (tt) parent.
If all the progeny show the dominant character, the plant is homozygous: $TT \times tt \rightarrow$ all Tt.
If the progeny show dominant and recessive characters in a 1 : 1 ratio, the plant is heterozygous: $Tt \times tt \rightarrow$ 1 Tt : 1 tt.
A back cross is a cross of the $F_1$ with either parent; only the cross with the recessive parent (the test cross) reveals the genotype.
Hence the genotype is determined by a test cross.
In a test cross the plant is crossed with the homozygous recessive (tt) parent.
If all the progeny show the dominant character, the plant is homozygous: $TT \times tt \rightarrow$ all Tt.
If the progeny show dominant and recessive characters in a 1 : 1 ratio, the plant is heterozygous: $Tt \times tt \rightarrow$ 1 Tt : 1 tt.
A back cross is a cross of the $F_1$ with either parent; only the cross with the recessive parent (the test cross) reveals the genotype.
Hence the genotype is determined by a test cross.