The nucleotide triplet CTC in the sixth position of the l3-chain in DNA forms the complementary nucleotide on (mRNA) that codes for glutamic acid. A point mutation on the l3-chain resulting in the nucleotide triplet CAC forms a complementary nucleotide on mRNA that codes for valine. In sickle cell anemia, you would expect the complementary nucleotide triplet on mRNA from 5&; to 3&; to read

**Core Concept:**
In the field of genetics, the relationship between DNA and mRNA is crucial for understanding genetic disorders like sickle cell anemia. DNA has a double helix structure with the genetic code written in nucleotide triplets, called codons. Each codon specifies a particular amino acid when translated into the corresponding mRNA molecule. In the given question, we focus on the l3-chain of DNA and its relationship with mRNA codons.

**Why the Correct Answer is Right:**
The correct answer is derived from the understanding of the genetic code and how it is translated into amino acids. In the case of sickle cell anemia, the mutation occurs in codon CAC (for valine) to CTA (for leucine). This is because the mutation changes the corresponding codon on the mRNA molecule. In the mRNA sequence from 5' to 3', the correct answer is:

**Correct Answer:** .

**Why Each Wrong Option is Incorrect:**

A. The nucleotides on the DNA molecule do not directly translate into the corresponding amino acids on the mRNA molecule. Instead, the genetic code specifies these relationships, which are then translated during transcription and translation processes.

B. The mRNA codon translates as the reverse of the corresponding nucleotide triplet on the DNA molecule. However, the mutation in this question is not a reverse mutation, so Option B is incorrect.

C. The mutation in the question involves changing the codon for valine to codon for leucine. The correct answer reflects this change, while Option C does not accurately represent the mutation's effect.

D. Similar to Option B, the mutation in the question is not a reverse mutation, making Option D incorrect.

**Clinical Pearl:**
In the context of sickle cell anemia, understanding these relationships between DNA, mRNA, and amino acids is crucial for understanding how genetic mutations can lead to disease and therapy. The correct answer highlights this relationship and demonstrates the effect of the mutation on the amino acid sequence. Remember, these concepts are fundamental for understanding genetic disorders and their treatment strategies.

✓ Correct Answer: D. GUG