A frameshift mutation occurs when one or more nucleotides are deleted or inserted into a DNA sequence, which alters the reading frame of the sequence. From the provided original sequence "AGC TTA TCG", we need to identify which of the options has a deletion that shifts the reading frame.
Let's analyze the responses:
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AGC TTA TAG - This doesn't have a deletion; it seems to be a change in the third codon.
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AGC TTA TAG - This is a repetition of the first option and also doesn't have a deletion.
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AGC TCG - This option has a deletion of 2 bases (the second T and the second A), which shifts the reading frame.
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AGC TTT CG - This option has an extra T added, which would not cause a frameshift by deletion.
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AGC TTT CG TTA TCG - This is not a single sequence, as it has an extra segment and does not reflect a simple deletion.
The correct option consistent with a frameshift mutation through deletion would be: AGC TCG.
This deletion results in a change to the downstream codon, which influences the translation of the entire sequence thereafter.