The genetic code is nonoverlapping, i.e.,the adjacent codons do not overlap. A nonoverlapping code means that the same letter is not used for two different codons. In other words, no single base can take part in the formation of more than one codon.
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For an overlapping code, consecutive amino acids are encoded in the mRNA by codons that share some consecutive bases; for example, the last two bases of one codon may also be the first two bases of the next codon.

Therefore : non overlapping = 6
overlapping = 18 for understanding sequence is
:ICU ACA ....
now as codons are overlapped , codons can be written as ICU CUA UAC ACA and so on
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Ans is option 3

Introduction:
The genetic code is the set of rules by which information stored in the genetic material (DNA or RNA sequences) is translated into proteins. Codons are sequences of three nucleotides in mRNA that specify the amino acids to be incorporated into a protein during translation. In this question, we are given an mRNA sequence and asked to determine the number of codons present when considering both non-overlapping and overlapping genetic codes.

Non-overlapping Genetic Code:
In the non-overlapping genetic code, each codon is read separately and does not overlap with the adjacent codons. Each codon specifies one amino acid. To determine the number of codons in the given mRNA sequence using the non-overlapping genetic code, we divide the total number of nucleotides by 3 (since each codon consists of 3 nucleotides).

The given mRNA sequence is: 5’-UCU ACA GUG AUC GUC ACC -3’
Counting the number of nucleotides, we have 21 nucleotides.
Dividing 21 by 3, we get 7 codons.

Therefore, the number of codons in this mRNA sequence using the non-overlapping genetic code is 7.

Overlapping Genetic Code:
In the overlapping genetic code, each nucleotide is part of multiple codons and can be read in different reading frames. This means that each nucleotide can be part of multiple codons, resulting in a higher number of codons compared to the non-overlapping genetic code.

To determine the number of codons in the given mRNA sequence using the overlapping genetic code, we need to consider all possible reading frames. A reading frame is defined as the way nucleotides are grouped into codons. Since a codon consists of three nucleotides, we need to check all possible reading frames that start at positions 1, 2, and 3 of the mRNA sequence.

Starting at position 1: UCU ACA GUG AUC GUC ACC
Number of codons = 7

Starting at position 2: CUA CAG UGA UCG UCA CC
Number of codons = 6

Starting at position 3: UAC AGU GAU CGU CCA
Number of codons = 5

Total number of codons considering all reading frames = 7 + 6 + 5 = 18

Therefore, the number of codons in this mRNA sequence using the overlapping genetic code is 18.

Conclusion:
The number of codons in the given mRNA sequence, considering the non-overlapping and overlapping genetic codes, are 7 and 18 respectively. This difference arises due to the different ways in which the nucleotides can be grouped into codons and read during translation. The overlapping genetic code allows for multiple reading frames, resulting in a higher number of possible codons compared to the non-overlapping genetic code.