Which of the following statements is/are incorrect?
I. Six codons do not code for any amino acid.
II. A codon is read in mRNA in a contiguous fashion.
III. Three codons function as stop codons.
IV. The initiator codon AUG codes for methionine.

The correct option is D I
A codon refers to a sequence of 3 consecutive nucleotides (triplet) in mRNA that codes for a specific amino acid or signals the termination of protein synthesis.

There are 64 such codons formed by permutation and combination of four RNA bases - A, U, G and C.

The codon 'AUG' codes for the amino acid methionine, acts as the initiator codon and begins the synthesis of polypeptide due to which it is also referred to as the start codon.

Of the 64 codons, three codons (UAA, UAG and UGA) do not specify any amino acid and are known as stop codons as the presence of any of the three stop codons causes termination of protein synthesis.

The codon is read in a contiguous fashion and there are no punctuations.

The amino acids arginine and leucine are coded by six codons each.

Hence, the statement I is incorrect.