Question

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.

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Test cross outcomes mapping:
All dominant offspring $\rightarrow$ Unknown parent is Homozygous dominant.
1:1 ratio of dominant to recessive $\rightarrow$ Unknown parent is Heterozygous.

Answer 1

The Correct Option is C

Step 1: Understanding the Problem:
A test cross is a genetic cross designed to determine whether an organism expressing a dominant phenotype is homozygous dominant or heterozygous.
Step 2: Approach and Formula:
Analyze the definition and the expected Mendelian segregation ratios of a typical test cross to validate both statements.
Step 3: Detailed Explanation:
- Statement I: The standard procedure for a test cross is to cross the organism with the dominant phenotype (whose genotype is unknown, either TT or Tt) with a homozygous recessive parent (tt). Thus, Statement I accurately defines the methodology and is true.
- Statement II: The statement claims that observing a ratio of dominant and recessive traits implies a homozygous dominant parent. This is incorrect. If the unknown parent were homozygous dominant (TT), crossing it with (tt) would yield 100% dominant offspring (Tt) in the F1 generation. There would be no recessive offspring at all.
Conversely, if a 1:1 ratio of dominant to recessive offspring appears, it proves the unknown parent is heterozygous (Tt). Thus, Statement II is false.
Step 4: Final Answer:
Statement I is true but Statement II is false.