**Question:** Total numbers of codons are -

A.
B.
C.
D.

**Correct Answer:** .

**Core Concept:**

Codons are triplet nucleotide sequences that specify the amino acid sequence during translation of a messenger RNA (mRNA) molecule into a protein. Amino acids are the building blocks of proteins, and the genetic code regulates the incorporation of these amino acids into the growing polypeptide chain. The genetic code consists of 64 codons, which can be grouped into three classes: start (AUG), stop (UAA, UAG, UGA), and sense (all others).

**Why the Correct Answer is Right:**

The correct answer is **D**. This is because the total number of codons in the genetic code is 64. The genetic code consists of three classes of codons: start (AUG), stop (UAA, UAG, UGA), and sense (all others). The sense codons represent the actual amino acid coding, and there are 61 of them (from AUG to UAG, excluding UAA, UAG, and UGA). Thus, the total number of codons is the sum of these three classes, which equals 64.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because it refers to the total number of codons as 63, which is less than the actual number (64).
B. This option is also incorrect because it refers to the total number of codons as 62, which is also less than the actual number (64).
C. This option is incorrect as it incorrectly states that the total number of codons is 60, which is even less than the actual number (64).

**Clinical Pearl:**

Understanding the genetic code and its codons is essential for medical students and practicing doctors, as it directly relates to the process of protein synthesis and translation in cells. This knowledge is particularly important in fields like molecular biology, genetics, and clinical genetics, where understanding genetic variations and mutations often involves counting codons and their implications.