To analyze the DNA segment "CCC ATA GCT" and determine which copy exhibits a deletion in the first codon triplet followed by a substitution mutation, let's first identify the first codon triplet.
The original sequence is:
- 1st codon: CCC
- 2nd codon: ATA
- 3rd codon: GCT
Step 1: Identify a deletion in the first codon triplet. This means that at least one base must be removed from "CCC". The possible deletions could result in either "CC", "C", or might even completely deplete the first codon.
Step 2: Identify a substitution mutation. After the deletion has been made, one or more bases might be substituted with another base.
Now, let’s examine the provided options:
a. CCC TAG CT:
- There's no deletion in "CCC"; thus, this doesn't fit.
b. CCA TAG CT:
- Here, "CCC" has changed to "CCA" (substitution), and the rest of the sequence has changed. "ATA" was deleted, and "GCT" appears to have been altered.
- This indicates a substitution and shows part of the first codon changed.
c. CCA TAA CT:
- "CCC" changed to "CCA" (substitution). "ATA" appears to still be deleted (making "TAA"), but it doesn't follow the steps straightforwardly.
d. CCA ATA GCT:
- "CCC" changed to "CCA," but there isn’t any deletion indicated, so this doesn’t fit.
Conclusion: The only option that fits the description of having a deletion in the first codon followed by a substitution is b. CCA TAG CT, since it shows a change in the first codon from CCC to CCA and a deletion of the second codon "ATA".