DNA Mutations Practice Worksheet showing original and mutated sequences with analysis.

The worksheet asks you to compare mutated DNA sequences to the original and determine what kind of mutation occurred — whether it’s a substitution, insertion, or deletion — and then explain how that change affects the resulting protein.

Let’s go step by step for each mutation:

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Original DNA Sequence:
TAC ACC TTG GCG ACG ACT

We first transcribe this into mRNA (replace T with U):
→ mRNA: AUG UGG AAC CGC UGC UGA

Then translate into amino acids using the genetic code:
- AUG → Methionine (Met) — start
- UGG → Tryptophan (Trp)
- AAC → Asparagine (Asn)
- CGC → Arginine (Arg)
- UGC → Cysteine (Cys)
- UGA → Stop

So original protein: Met - Trp - Asn - Arg - Cys - [Stop]

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Mutation #1:
DNA: TAC ACC TTG GCG ACT ACT
(Compare to original: last codon changed from ACG to ACT)

Transcribe to mRNA: AUG UGG AAC CGC UGA UGA
Wait — let’s be careful.

Original DNA: TAC ACC TTG GCG ACG ACT
Mutated DNA: TAC ACC TTG GCG ACT ACT

So only the 5th codon changed: ACG → ACT

mRNA for mutated: AUG UGG AAC CGC UGU UGA
(Assuming we read in triplets: positions 1-3, 4-6, etc.)

Actually, let’s write it properly:

Original DNA: TAC ACC TTG GCG ACG ACT
→ mRNA: AUG UGG AAC CGC UGC UGA

Mutated DNA: TAC ACC TTG GCG ACT ACT
→ mRNA: AUG UGG AAC CGC UGU UGA

Now translate:

AUG → Met
UGG → Trp
AAC → Asn
CGC → Arg
UGU → Cysteine (same as UGC!)
UGA → Stop

So protein is still: Met - Trp - Asn - Arg - Cys - [Stop]

No change in amino acid! That’s because both UGC and UGU code for Cysteine.

This is a silent mutation — specifically a substitution (one base replaced another), but no effect on protein.

In the worksheet, they ask:
- Type of mutation: Substitution
- Effect on protein: No change (silent)

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Mutation #2:
DNA: TAC GAC CTT GGC GAC ACT
Compare to original: TAC ACC TTG GCG ACG ACT

Look at position 2: ACC → GAC → that’s a substitution (C→G in second base of second codon)

But also look further: original has TTG GCG, mutated has CTT GGC — seems like there’s a shift?

Wait — let’s align them:

Original: TAC ACC TTG GCG ACG ACT
Mutated: TAC GAC CTT GGC GAC ACT

It looks like after the first codon, everything shifted? Let’s check length.

Original: 6 codons = 18 bases
Mutated: also 18 bases? Let’s count:

TAC GAC CTT GGC GAC ACT → 6 codons → 18 bases → same length.

But let’s transcribe:

Original mRNA: AUG UGG AAC CGC UGC UGA
Mutated DNA: TAC GAC CTT GGC GAC ACT
→ mRNA: AUG CUG GAA CCG CUG ACU ? Wait — that doesn’t match.

Actually, if DNA is TAC GAC CTT GGC GAC ACT, then mRNA is:

AUG CUG GAA CCG CUG ACU

But original was AUG UGG AAC CGC UGC UGA

So comparing:

Position 2: UGG → CUG → Trp → Leu → different amino acid
Position 3: AAC → GAA → Asn → Glu → different
Position 4: CGC → CCG → Arg → Pro → different
Position 5: UGC → CUG → Cys → Leu → different
Position 6: UGA → ACU → Stop → Thr → now not stop!

This is messy. But notice: the sequence “TTG GCG” became “CTT GGC” — which suggests a frameshift? But total bases are same.

Wait — actually, looking closely:

Original: TAC ACC TTG GCG ACG ACT
Mutated: TAC GAC CTT GGC GAC ACT

If we break into codons:

Original: TAC | ACC | TTG | GCG | ACG | ACT
Mutated: TAC | GAC | CTT | GGC | GAC | ACT

So each codon after the first is different — but no bases added or deleted. So it’s multiple substitutions? Or perhaps a single event?

Actually, this looks like a deletion of one base followed by an insertion? But the worksheet likely intends this to be a frameshift mutation due to deletion or insertion.

Wait — let’s recount the bases between original and mutated.

Original: TAC ACC TTG GCG ACG ACT → 18 bases
Mutated: TAC GAC CTT GGC GAC ACT → also 18 bases? Let’s spell:

T-A-C-G-A-C-C-T-T-G-G-C-G-A-C-A-C-T → that’s 18 characters.

But if you look at the sequence, it seems like the “ACC” became “GAC”, and “TTG” became “CTT”, etc. — but that would require multiple point mutations.

However, in the context of this worksheet, and given the handwritten answers, it appears the intended interpretation is that this is a deletion of one base early on, causing a frameshift.

Looking at the mutated DNA: TAC GAC CTT GGC GAC ACT

If we assume the original was TAC ACC TTG GCG ACG ACT, and mutated is TAC GAC CTT GGC GAC ACT, perhaps there was a deletion of the second ‘C’ in “ACC”, making it “AC”, then the next base ‘T’ from “TTG” shifts in, so “ACT” becomes the second codon? But that doesn’t match.

Alternatively, maybe it’s a deletion of the first ‘A’ in “ACC”? Let’s try:

Original: TAC ACC TTG GCG ACG ACT
Remove the ‘A’ from position 5 (second codon first base): TAC CC TTG GCG ACG ACT → then group: TAC CCT TGG CGA CGA CT... messy.

Perhaps the worksheet has a typo, or the student miswrote.

But looking at the handwritten answer in the image for Mutation #2, it says:

“Protein: Met - Asp - Leu - Gly - Asp - Thr”

And type: Substitution? But that doesn’t make sense with the sequence.

Wait — let’s transcribe the mutated DNA as written: TAC GAC CTT GGC GAC ACT

mRNA: AUG CUG GAA CCG CUG ACU

Translate:

AUG → Met
CUG → Leu
GAA → Glu
CCG → Pro
CUG → Leu
ACU → Thr

So protein: Met - Leu - Glu - Pro - Leu - Thr

But the handwritten answer says “Met - Asp - Leu - Gly - Asp - Thr” — which doesn’t match.

Asp is GAU/GAC, Leu is UUA/UUG/CUU/CUC/CUA/CUG, Gly is GGU/GGC/GGA/GGG, etc.

So if mRNA is AUG CUG GAA CCG CUG ACU, amino acids are Met-Leu-Glu-Pro-Leu-Thr.

But the handwritten answer says Met-Asp-Leu-Gly-Asp-Thr — which would require mRNA: AUG GAU CUG GGU GAU ACU or something.

This suggests the mutated DNA might be different.

Perhaps the mutated DNA is meant to be: TAC GAC CTT GGC GAC ACT — but if we read it as:

TAC | GAC | CTT | GGC | GAC | ACT

mRNA: AUG | CUG | GAA | CCG | CUG | ACU

Amino acids: Met | Leu | Glu | Pro | Leu | Thr

But the worksheet's handwritten answer says "Met - Asp - Leu - Gly - Asp - Thr" — which is incorrect based on the DNA given.

Unless... perhaps the DNA is TAC GAC CTT GGC GAC ACT, but when transcribed, if we consider that "GAC" in DNA is "CUG" in mRNA, which is Leu, not Asp.

Asp is coded by GAU or GAC in mRNA, which comes from CTA or CTG in DNA.

I think there might be a mistake in the worksheet or in the student's transcription.

But for the sake of this exercise, let's assume the mutated DNA is as written, and we transcribe correctly.

However, looking back at the image, for Mutation #2, the DNA is written as "TAC GAC CTT GGC GAC ACT", and the student wrote "Met - Asp - Leu - Gly - Asp - Thr", which is wrong.

Perhaps it's a different mutation.

Another possibility: maybe it's a deletion of one base.

Let's try deleting the second base 'A' from the original DNA.

Original: TAC ACC TTG GCG ACG ACT
Delete position 2 (the 'A' in "ACC"): TAC CCT TGG CGA CGA CT... then group as TAC CCT TGG CGA CGA CT — but that's 17 bases, not divisible by 3.

Delete the first 'C' in "ACC": TAC ACT TGG CGA CGA CT — still 17 bases.

Perhaps delete the 'T' from "TTG": TAC ACC TG GCG ACG ACT — then TAC ACC TGG CGA CGA CT — 17 bases.

This is not working.

Perhaps the mutated DNA is meant to be shorter or longer.

Let's count the bases in the mutated DNA as written in the image: "TAC GAC CTT GGC GAC ACT" — that's 6 groups of 3, so 18 bases.

But in the handwritten answer, the protein has 6 amino acids, so it's in frame.

Perhaps it's a series of substitutions.

But the worksheet asks for "type of mutation" and lists options like "substitution", "insertion", "deletion".

For Mutation #2, if we compare:

Original: TAC ACC TTG GCG ACG ACT
Mutated: TAC GAC CTT GGC GAC ACT

The changes are:
- Codon 2: ACC -> GAC (A->G in first position)
- Codon 3: TTG -> CTT (T->C in first position, and G->T in third? TTG to CTT is T->C and G->T, but also the order is different — TTG vs CTT, which is not just a substitution; it's like the codon is reversed or something.

TTG is Leu, CTT is also Leu, but in DNA, TTG is T-T-G, CTT is C-T-T, so different bases.

This is confusing.

Perhaps it's a frameshift due to deletion.

Let's assume that in Mutation #2, there is a deletion of one base.

Suppose we delete the 'A' from "ACC" in the original.

Original: TAC ACC TTG GCG ACG ACT
After deleting the 'A' at position 5: TAC CCT TGG CGA CGA CT — but that's 17 bases.

Then group as: TAC CCT TGG CGA CGA CT — but 17 bases, so last codon incomplete.

mRNA: AUG GGA CCA GGC UGC U... not good.

Perhaps delete the 'C' from "TTG": TAC ACC TG GCG ACG ACT — then TAC ACC TGG CGA CGA CT — 17 bases.

Still not good.

Another idea: perhaps the mutated DNA is "TAC GAC CTT GGC GAC ACT" but it's meant to be compared as having a deletion in the middle.

Let's look at the sequence: original has "TTG GCG", mutated has "CTT GGC" — which is like the "TTG" became "CTT" and "GCG" became "GGC", which could be if a base was deleted and inserted, but it's complicated.

Perhaps for the purpose of this worksheet, we should go with the handwritten answer or the standard interpretation.

In many such worksheets, Mutation #2 is often a frameshift due to deletion.

Let's try this: suppose in the original DNA, we delete the 'T' from "TTG", so it becomes "TG", then the next bases shift.

Original: TAC ACC TTG GCG ACG ACT
Delete the first 'T' of "TTG": so positions 7-9 were TTG, now we have TG from position 7-8, then GCG from 10-12, etc.

So new sequence: TAC ACC TG GCG ACG ACT — but that's TAC ACC TGG CGA CGA CT — let's write it:

Positions: 1-3: TAC, 4-6: ACC, 7-8: TG, 9-11: GCG, 12-14: ACG, 15-17: ACT — but 17 bases, so not divisible by 3.

To make it work, perhaps delete a base so that the reading frame shifts.

Assume we delete the 'A' from "ACC" (position 5).

Original: TAC ACC TTG GCG ACG ACT
After deletion: TAC CCT TGG CGA CGA CT — 17 bases.

Then mRNA: AUG GGA CCA GGC UGC U...

Translate: AUG (Met), GGA (Gly), CCA (Pro), GGC (Gly), UGC (Cys), U... incomplete.

Not matching.

Perhaps the mutated DNA is "TAC GAC CTT GGC GAC ACT" and it's a substitution mutation for each codon, but that would be multiple substitutions, which is unlikely.

Let's calculate the amino acid sequence for the mutated DNA as written:

DNA: TAC GAC CTT GGC GAC ACT
mRNA: AUG CUG GAA CCG CUG ACU
Amino acids: Met, Leu, Glu, Pro, Leu, Thr

But the handwritten answer says "Met - Asp - Leu - Gly - Asp - Thr" — which is incorrect.

Asp is GAU/GAC, so for Asp, mRNA must have GAU or GAC, which means DNA has CTA or CTG.

In the mutated DNA, "GAC" is present, which is DNA for CUG in mRNA, which is Leu, not Asp.

So the student's answer is wrong.

For Mutation #3:

DNA: TAC GAC CTT GGC GAC T (only 17 bases? Let's see: TAC GAC CTT GGC GAC T — that's 5 full codons and one base, so 16 bases? T-A-C-G-A-C-C-T-T-G-G-C-G-A-C-T — 16 bases.

Original is 18 bases, so this is a deletion of 2 bases.

Mutated DNA: TAC GAC CTT GGC GAC T — 16 bases.

So likely a deletion of 2 bases, causing frameshift.

Transcribe: since 16 bases, mRNA will be 16 bases, so 5 full codons and 2 bases left over.

mRNA: AUG CUG GAA CCG CUG AC — then stop or something.

Amino acids: AUG (Met), CUG (Leu), GAA (Glu), CCG (Pro), CUG (Leu), and AC is incomplete.

So protein: Met-Leu-Glu-Pro-Leu — and then no stop, or truncated.

The handwritten answer says "Met - Asp - Leu - Gly - Asp" and "no stop codon".

Again, Asp is not correct; it should be Leu for CUG.

So there are errors in the student's work.

For the final answer, since the user asked to solve the problem, and the worksheet has three mutations, I need to provide the correct analysis.

But the user's instruction is to provide the final answer after reasoning, and the options are false, so no explanation or teaching.

Perhaps for this response, since the task is to solve the problem, and the problem is to fill in the worksheet, I should provide the correct entries for each mutation.

Let's do that.

For Mutation #1:
DNA: TAC ACC TTG GCG ACT ACT
- This is a substitution (ACG -> ACT in DNA, which is UGC -> UGU in mRNA, both code for Cysteine)
- Protein: Met-Trp-Asn-Arg-Cys-Stop (same as original)
- Type: Substitution
- Effect: Silent mutation (no change in protein)

For Mutation #2:
DNA: TAC GAC CTT GGC GAC ACT
- This appears to be a series of substitutions, but let's assume it's intended to be a frameshift. However, with 18 bases, it's in frame.
- mRNA: AUG CUG GAA CCG CUG ACU
- Protein: Met-Leu-Glu-Pro-Leu-Thr
- Compared to original Met-Trp-Asn-Arg-Cys-Stop, this is completely different.
- Type: Since all codons are changed, it could be multiple substitutions, but typically in such worksheets, if the sequence is shifted, it's a frameshift. Here, it's not shifted; it's different codons.
- Perhaps it's a deletion of one base and insertion of another, but that's complex.
- Given the context, and that the student wrote "substitution", but it's not accurate, I think for this, it's best to say it's a substitution mutation for each codon, but that's not standard.
- Another possibility: perhaps "GAC" in DNA is meant to be "GTC" or something.
- Let's look at the sequence: original has "ACC TTG GCG", mutated has "GAC CTT GGC" — which is like the "ACC" became "GAC", "TTG" became "CTT", "GCG" became "GGC" — each codon has a different first base or something.
- This is not a single mutation; it's multiple.
- For the sake of this, I'll assume it's a substitution mutation, and the protein is changed.
- But to match the worksheet's intent, perhaps it's a frameshift due to deletion.
- Let's calculate the number of bases: both have 18, so no frameshift.
- So it must be a substitution mutation.
- Type: Substitution
- Effect: Missense or nonsense, but here it's missense for several codons, and the stop codon is changed to Thr, so no stop, which is bad.
- In this case, the protein is longer or truncated? Here, the last codon is ACU, which is Thr, not stop, so the ribosome would continue until it hits a stop codon, but in this sequence, there is no stop codon, so it would be a longer protein or truncated if it hits a stop later, but in this fragment, it's Met-Leu-Glu-Pro-Leu-Thr, and no stop, so it's incomplete.
- Original has stop at the end, this does not, so it's a nonsense mutation? No, nonsense is when a stop codon is created; here, a stop codon is removed, so it's a loss of stop codon.
- Type: Substitution (since bases are replaced, not added or deleted)
- Effect: The protein is longer than normal because the stop codon is changed to an amino acid codon.

But in the sequence, the last codon is ACT in DNA, which is ACU in mRNA, Thr, not stop. Original was ACT, which is ACU, but in original, the last codon is ACT, which is ACU, Thr? No!

I think I made a mistake.

Original DNA: TAC ACC TTG GCG ACG ACT

Let's transcribe carefully:

DNA: TAC ACC TTG GCG ACG ACT

mRNA: AUG UGG AAC CGC UGC UGA

UGA is stop codon.

In Mutation #1: DNA: TAC ACC TTG GCG ACT ACT

mRNA: AUG UGG AAC CGC UGU UGA (since ACT in DNA is ACU in mRNA, but here it's ACT for the last codon? Let's see:

Positions: 1-3: TAC -> AUG
4-6: ACC -> UGG
7-9: TTG -> AAC
10-12: GCG -> CGC
13-15: ACT -> UGU (because ACT in DNA is ACU in mRNA, which is Cys)
16-18: ACT -> UGA (stop)

So protein: Met-Trp-Asn-Arg-Cys-Stop — same as original, since UGC and UGU both code for Cys.

For Mutation #2: DNA: TAC GAC CTT GGC GAC ACT

mRNA: AUG CUG GAA CCG CUG ACU

Amino acids: Met (AUG), Leu (CUG), Glu (GAA), Pro (CCG), Leu (CUG), Thr (ACU)

No stop codon, so the protein would be longer if there are more bases, but in this fragment, it's 6 amino acids, no stop.

Compared to original, which has stop at position 6, this has Thr at position 6, so it's a change from stop to Thr, which means the protein will continue until a stop codon is encountered, so it's a loss of stop codon.

Type: Substitution (bases are replaced)

Effect: The protein is longer than normal.

For Mutation #3: DNA: TAC GAC CTT GGC GAC T (16 bases)

So likely a deletion of 2 bases.

mRNA: AUG CUG GAA CCG CUG AC (16 bases)

Amino acids: Met, Leu, Glu, Pro, Leu, and then AC is incomplete, so only 5 full amino acids, and no stop codon.

Type: Deletion (of 2 bases)

Effect: Frameshift, protein is truncated and may not function.

Now, for the final answer, since the user didn't specify what to output, but the task is to solve the problem, and the problem is to fill in the worksheet, I think the final answer should be the correct entries for each mutation.

But the user said "provide the final correct answer", so perhaps for each mutation, state the type and effect.

Since the response format requires a final answer after reasoning, and no options are true, I'll provide the corrected analysis.

Final Answer:
For Mutation #1: Substitution; silent mutation (no change in protein).
For Mutation #2: Substitution; loss of stop codon (protein is longer than normal).
For Mutation #3: Deletion; frameshift mutation (protein is truncated and nonfunctional).

But to match the worksheet's format, perhaps list it as:

Mutation #1: Type: Substitution, Effect: No change in protein
Mutation #2: Type: Substitution, Effect: Protein is longer (loss of stop codon)
Mutation #3: Type: Deletion, Effect: Frameshift, protein truncated

However, in Mutation #2, if it's a substitution, and the stop codon is changed, it's correct.

In the student's work, for Mutation #2, they said "substitution" and "protein is longer", which is correct for the sequence given, even though the amino acid sequence they wrote is wrong.

For Mutation #3, they said "deletion" and "no stop codon", which is correct.

So perhaps the final answer is as per the student's type, but with correct effects.

I think for accuracy, I'll go with:

Final Answer:
Mutation #1: Substitution; silent mutation (amino acid sequence unchanged)
Mutation #2: Substitution; loss of stop codon (protein will be longer than normal)
Mutation #3: Deletion; frameshift mutation (protein is truncated and likely nonfunctional)