Question

Given below are two statements :
one is labelled as
Assertion (A) and the other is labelled as
Reason (R).
Assertion (A) :
The closer two loci reside along the axis of the chromosome, the more likely they are to be inherited together.
Reason (R) :
The farther apart two linked loci, the more likely a random crossover event will occur in between them.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Remember: \[ \text{Recombination frequency} \propto \text{Distance between genes} \]
• Closely linked genes \(\rightarrow\) inherited together
• Widely separated genes \(\rightarrow\) more recombination \[ 1\% \text{ recombination} = 1 \text{ map unit (centimorgan)} \]

Answer 1

The Correct Option is A

Concept: Genes located on the same chromosome are called: \[ \text{Linked genes} \] Linked genes tend to be inherited together. However, crossing over during meiosis can separate linked genes. The probability of crossing over depends on the distance between loci:
• Closely located genes \(\rightarrow\) lower chance of crossover
• Distant genes \(\rightarrow\) higher chance of crossover Thus, recombination frequency increases with increasing distance between genes.

Step 1: Evaluating Assertion (A). The assertion states: \[ \text{Closer loci are more likely to be inherited together} \] This statement is correct because closely linked genes are less likely to be separated by crossing over. Therefore: \[ \boxed{(A) \text{ is correct}} \]

Step 2: Evaluating Reason (R). The reason states: \[ \text{Farther apart linked loci have higher probability of crossover between them} \] This statement is also correct. As physical distance between loci increases: \[ \text{Chance of recombination increases} \] Hence: \[ \boxed{(R) \text{ is correct}} \]

Step 3: Determining whether (R) explains (A). The reason directly explains the assertion because:
• Closely spaced genes rarely undergo crossover.
• Therefore, they are inherited together more frequently. Thus: \[ \boxed{(R) \text{ is the correct explanation of } (A)} \] Therefore, the correct answer is: \[ \boxed{(A)\ \text{Both (A) and (R) are correct and (R) is the correct explanation of (A)}} \]