Mutations Worksheet Key - Deletion, Insertion and Substitution ... - Free Printable

Let’s go step by step through each mutated DNA sequence and figure out what kind of mutation it is, what the mRNA and amino acid sequences become, and whether there will likely be effects.

We are given the original:

Original DNA Sequence:
T A C A C C T T G G C G A C G A C T ...

→ Remember: DNA → mRNA (replace T with U, and complement base pairing: A↔U, T↔A, C↔G, G↔C)

So original mRNA:
A U G / U G G / A A C / C G C / U G C / U G A

Break into codons (groups of 3):

- AUG → Methionine (start)
- UGG → Tryptophan
- AAC → Asparagine
- CGC → Arginine
- UGC → Cysteine
- UGA → Stop

So amino acid sequence:
Methionine - Tryptophan - Asparagine - Arginine - Cysteine - Stop

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Now let’s do each mutated sequence one by one.

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Mutated DNA Sequence #1:

T A C A T C T T G G C G A C G A C T ...

Compare to original:
Original: T A C A C C T T G G C G A C G A C T
Mutant #1: T A C A T C T T G G C G A C G A C T
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑......Wait — actually, let's align them properly.

Original:
Position: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20...
DNA: T A C A C C T T G G C G A C G A C T ...

Mutant #1:
T A C A T C T T G G C G A C G A C T ...

So at position 5: Original has C, mutant has T → that’s a substitution.

But wait — let’s check the full alignment:

Original: T A C A C C T T G G C G A C G A C T
Mutant #1: T A C A T C T T G G C G A C G A C T
Positions 1-4 same. Position 5: C→T. Then rest same? Let’s count:

Actually, looking again — in Mutant #1, after “TACAT” instead of “TACAC”, so yes — position 5 changed from C to T → substitution.

BUT — look at the answer key provided in the image: for Mutant #1, they say mRNA is AUG/UAG/... and amino acid is Methionine-Stop → which means the second codon became UAG (stop).

How did that happen?

Let’s transcribe Mutant #1 DNA to mRNA:

DNA: T A C A T C T T G G C G A C G A C T ...

mRNA: A U G U A G A A C C G C U G C U G A ...

Codons:

- AUG → Methionine
- UAG → STOP ← this is the change!
- AAC → Asparagine (but we stop here)
- etc.

So why did UAG appear? Because in DNA, position 5 was changed from C to T → so in mRNA, position 5 becomes A (since DNA T → mRNA A), but wait — let’s map carefully.

Original DNA positions 4-6: A C C → mRNA: U G G

Mutant #1 DNA positions 4-6: A T C → mRNA: U A G

Yes! So the second codon changed from UGG (Tryptophan) to UAG (Stop). That’s a nonsense mutation — because a substitution created a stop codon.

And since it’s a substitution that creates a stop → Nonsense

Also, effects? YES — protein stops early → very bad.

✔ Matches the key: Nonsense

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Mutated DNA Sequence #2:

T A C G A C C T T G G C G A C G A C T ...

Compare to original:

Original: T A C A C C T T G G C G A C G A C T
Mutant #2: T A C G A C C T T G G C G A C G A C T

Look at position 4: Original has A, mutant has G → substitution? But wait — let’s see length.

Original starts: T A C A C C ... (positions 1-6)

Mutant #2: T A C G A C C ... → that’s 7 bases already? Wait no — let’s write aligned:

Original: T A C A C C T T G G C G A C G A C T
Mutant #2: T A C G A C C T T G G C G A C G A C T

Ah! At position 4: Original has A, mutant has G → but then mutant has an extra base? Let’s count:

Original first 6: T A C A C C → 6 bases

Mutant #2 first 7: T A C G A C C → 7 bases? No — actually, if you look closely, mutant #2 has an extra "G" inserted after position 3? Let’s index:

Position: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20...

Original: T A C A C C T T G G C G A C G A C T ...

Mutant #2: T A C G A C C T T G G C G A C G A C T ...

Wait — actually, comparing:

After “TAC”, original has “ACC”, mutant has “GACC” — so it looks like a G was inserted after position 3.

Original: pos4=A, pos5=C, pos6=C

Mutant #2: pos4=G, pos5=A, pos6=C, pos7=C → so yes, insertion of G at position 4? Or rather, between pos3 and pos4?

Actually, standard way: if you insert a base, everything shifts.

So original DNA: T A C | A C C | T T G | G C G | A C G | A C T ...

Mutant #2: T A C | G A C | C T T | G G C | G A C | G A C | T ...

So the insertion is a G right after the third base (after “TAC”), making the fourth base G, pushing everything else right.

This is an insertion → causes frameshift.

Now transcribe to mRNA:

DNA: T A C G A C C T T G G C G A C G A C T ...

mRNA: A U G C U G G A A C C G C U G C U G A ...

Codons:

- AUG → Met
- CUG → Leu
- GAA → Glu
- CCG → Pro
- CUG → Leu
- CUG → Leu
- A... (incomplete)

Original amino acids: Met-Trp-Asn-Arg-Cys-Stop

New: Met-Leu-Glu-Pro-Leu-Leu-... → completely different after first amino acid → frameshift mutation

Type: Insertion → always frameshift → so Insertion (and implicitly frameshift)

Effects? YES — whole protein changed.

✔ Matches key: Insertion

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Mutated DNA Sequence #3:

T A C A C C T T A G C G A C G A C T ...

Compare to original:

Original: T A C A C C T T G G C G A C G A C T
Mutant #3: T A C A C C T T A G C G A C G A C T

At position 9: Original has G, mutant has A → substitution.

Transcribe to mRNA:

DNA: T A C A C C T T A G C G A C G A C T ...

mRNA: A U G U G G A A U C G C U G C U G A ...

Codons:

- AUG → Met
- UGG → Trp
- AAU → Asn (same as original AAC? Wait — original third codon was AAC → Asn; now AAU → also Asn!)

Because both AAC and AAU code for Asparagine → silent mutation

Fourth codon: CGC → Arg (same as original)

Fifth: UGC → Cys

Sixth: UGA → Stop

So amino acid sequence unchanged: Met-Trp-Asn-Arg-Cys-Stop

No effect → silent mutation.

✔ Matches key: Silent

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Mutated DNA Sequence #4:

T A C A C C T T G G C G A C T A C T ...

Compare to original:

Original: T A C A C C T T G G C G A C G A C T
Mutant #4: T A C A C C T T G G C G A C T A C T

At position 15: Original has G, mutant has T → substitution.

Transcribe to mRNA:

DNA: T A C A C C T T G G C G A C T A C T ...

mRNA: A U G U G G A A C C G C U G A U G A ...

Codons:

- AUG → Met
- UGG → Trp
- AAC → Asn
- CGC → Arg
- UGA → STOP ← here! Originally this was UGC (Cys), now UGA (Stop)
- Then UGA again? But we stop at first UGA.

So amino acid sequence: Met-Trp-Asn-Arg-STOP

Originally: Met-Trp-Asn-Arg-Cys-Stop → now missing Cys, stops earlier.

This is a substitution that changed Cys codon (UGC) to Stop (UGA) → nonsense mutation

Effects? YES — truncated protein.

✔ Matches key: Nonsense

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All match the provided key.

Final Answer: The worksheet answers are correctly filled as shown in the image. Each mutation type and its consequence have been accurately identified based on comparing the mutated DNA to the original, transcribing to mRNA, translating to amino acids, and classifying the mutation type according to definitions (deletion, insertion, substitution → leading to frameshift, missense, silent, or nonsense). Specifically:

- Mutant #1: Substitution → Nonsense (creates premature stop)
- Mutant #2: Insertion → Frameshift (alters reading frame)
- Mutant #3: Substitution → Silent (no amino acid change)
- Mutant #4: Substitution → Nonsense (creates premature stop)

All classifications and predicted effects (“Yes!” or “No!”) are correct per genetic code rules.