Q24 / 240 · KCET 2026 · Biology
Read the following statements.
Statement I: In a typical test cross, an organism showing a dominant phenotype is crossed with the recessive parent.
Statement II: The ratio of organisms showing dominant and recessive traits in $F_1$ generation of a test cross indicates that the organism with unknown genotype is homozygous dominant.
Choose the correct option.
Statement I: In a typical test cross, an organism showing a dominant phenotype is crossed with the recessive parent.
Statement II: The ratio of organisms showing dominant and recessive traits in $F_1$ generation of a test cross indicates that the organism with unknown genotype is homozygous dominant.
Choose the correct option.
- ABoth Statement I and Statement II are true
- BBoth Statement I and Statement II are false
- Correct answerCStatement I is true but Statement II is false
- DStatement I is false but Statement II is true
Solution
Statement I is true because a test cross is performed to determine the genotype of an organism exhibiting a dominant phenotype by crossing it with a homozygous recessive parent.
Statement II is false because if the $F_1$ generation of a test cross produces both dominant and recessive phenotypes (typically in a $1:1$ ratio), it indicates that the organism with the unknown genotype is heterozygous, not homozygous dominant. If the unknown organism were homozygous dominant, all $F_1$ offspring would exhibit only the dominant phenotype.
Answer: Statement I is true but Statement II is false
Statement II is false because if the $F_1$ generation of a test cross produces both dominant and recessive phenotypes (typically in a $1:1$ ratio), it indicates that the organism with the unknown genotype is heterozygous, not homozygous dominant. If the unknown organism were homozygous dominant, all $F_1$ offspring would exhibit only the dominant phenotype.
Answer: Statement I is true but Statement II is false
Hence, the correct answer is option: 'C'.