Question

Assertion (A): Repetitive sequences are stretches of DNA sequences that are thought to have no direct coding functions.
Reason (R): They shed light on chromosome structure, dynamics and evolution.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

When evaluating non-coding DNA questions, remember that a sequence's biochemical function (or lack thereof) is completely independent of its value as a research tool for scientists. Since both facts are true but describe different aspects of genomics, the answer defaults to option (B).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question addresses the characteristics and scientific significance of repetitive DNA sequences as documented during the Human Genome Project (HGP). We need to determine if both statements are true and if they share a direct cause-and-effect relationship.

Step 2: Key Formula or Approach:
* Repetitive DNA: Genomic segments containing sequences of nucleotide bases that are repeated multiple times, ranging from tens to hundreds of times across the genome.
* They make up a large portion of the human genome, but most do not encode functional proteins. Instead, they serve as structural and evolutionary markers.

Step 3: Detailed Explanation:
Evaluating Assertion (A): Findings from the Human Genome Project showed that a large fraction of the human genome consists of repetitive sequences. These segments do not translate into proteins and have no direct coding function. They are often spread across non-coding introns or structural regions like centromeres and telomeres. Thus, Assertion (A) is true.
Evaluating Reason (R): Even though they do not code for proteins, repetitive sequences are highly valued in molecular biology. Comparing these sequences across individuals and species provides critical insights into chromosomal organization, the mechanics of cell division (dynamics), and ancestral evolutionary paths. Thus, Reason (R) is also true.
* Evaluating the Link: Let's read the two statements together with the connector "because": "Repetitive sequences are thought to have no direct coding functions because they shed light on chromosome structure, dynamics, and evolution." This connection is logically incorrect. The lack of a coding function is a property of their genetic nature (they do not recruit transcription factor complexes or contain open reading frames for translation). It is not caused by the fact that scientists use them to study chromosome evolution. Both statements are independent genetic facts established by genomic research.
Since both statements are true but the reason does not explain the assertion, option (B) is the correct choice.

Step 4: Final Answer:
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A), matching option (B).