Question

Given below are two statements:
Statement I : Two-point test cross is used to know the linkage and map distance between genes
Statement II : Three-point test cross is performed to know the map distance and order of the genes on the chromosome
In light of the above statements, choose the most appropriate answer from the options given below:

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

Hint:

Two-point test cross establishes linkage and distance between 2 genes; Three-point test cross establishes distance AND linear gene order.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Genetic mapping uses testcross progeny frequencies to establish gene linkage, distance, and linear gene order.

Step 2: Detailed Explanation:
1. Statement I is TRUE: A two-point test cross ($AaBb \times aabb$) determines whether two loci are genetically linked and measures the recombination frequency/map distance (in centimorgans, cM) between them.
2. Statement II is TRUE: A three-point test cross ($AaBbCc \times aabbcc$) simultaneously determines the recombination distances across two adjacent intervals, uncovers double crossover events, and definitively establishes the linear gene order of the three loci on the chromosome.

Step 3: Final Answer:
Therefore, both Statement I and Statement II are true.