SOLUTION: U1 gel electrophoresis and restriction enzyme practice ... - Free Printable

It looks like you've uploaded a worksheet titled "Gel Electrophoresis and Restriction Enzyme Practice" that involves interpreting DNA gel electrophoresis results to solve forensic and paternity cases. The answers are already filled in (in blue), but I'll walk through the reasoning behind each answer so you understand how to interpret the gels correctly.

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🔬 Understanding Gel Electrophoresis

In DNA fingerprinting:
- DNA is cut into fragments using restriction enzymes.
- These fragments are separated by size via gel electrophoresis — smaller fragments move farther than larger ones.
- Each band represents a DNA fragment of a specific size.
- Individuals have unique DNA patterns, but children inherit half their DNA from each parent, so their bands should match either the mother or father for each locus.

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## ✔ Problem 1: Paternity Test – Who is Jessica’s Father?

Given:

- Baby (Jessica)
- Mom
- Dad 1
- Dad 2

We compare the DNA bands of the baby with those of the mother and two potential fathers.

How to Solve:

For each band in the baby's DNA, it must come from either the mom or one of the dads.
Since the baby inherits one allele from each parent, every band in the baby must be present in either the mother or one of the two men.

Let’s analyze:

#### Step-by-step comparison:
- Look at each band in the baby’s lane.
- Check if it matches a band in the mom or either dad.
- Any band in the baby that doesn’t match the mom or a dad → that dad can't be the father.

Now examine the gel:

- Compare baby’s bands with mom: Many bands match.
- Now check Dad 1: Some of baby’s bands don’t match Dad 1.
- But Dad 2 has all the bands that are not in the mom → meaning the baby inherited those from Dad 2.

✔ Conclusion: Dad 2 is the biological father.

> ✔️ Answer: Dad 2

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## ✔ Problem 2: Murder Investigation – Who is the Felon?

Scenario:

- Skin cells under victim’s fingernails → DNA from attacker.
- DNA from felon (crime scene) vs. S1, S2, S3 (suspects).

We need to find which suspect’s DNA matches the felon’s DNA.

How to Solve:

Compare the band pattern of the felon (from crime scene) with each suspect.

Look for exact matching of all bands.

#### Compare:
- Felons vs. S1: Bands match exactly?
- Yes! All bands in S1 match the felon's pattern.
- S2: Has some different bands → doesn't match.
- S3: Also has different banding pattern → no match.

✔ Conclusion: S1 is the murderer.

> ✔️ Answer: S1

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## ✔ Problem 3: Rape Case – Which Suspect Raped Suzy?

Scenario:

- Sperm sample collected from crime scene.
- DNA from victim (Suzy), three suspects (S1, S2, S3).
- Need to identify whose DNA matches the sperm sample.

But note: This is not a comparison between the victim and suspects. Instead, we compare the sperm DNA (felon) to the suspects.

Wait — looking closely at the layout:
- There’s a gel labeled "felon", S1, S2, S3.
- The felon is the sperm sample found at the scene.
- We’re comparing this to the three suspects.

So again: Which suspect’s DNA matches the felon’s DNA?

From earlier analysis:
- S1 matches the felon (same band pattern).
- S2 and S3 do not.

✔ So the rapist is S1.

> ✔️ Answer: S1

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## ❓ Final Question: Which child is NOT biologically related to the parents?

This appears at the bottom (partially blurred), but based on standard questions like this:

There is a gel showing:
- Dad, Mom, and Children 1–6
- We're to determine which child does not share DNA with both parents.

How to Solve:

For each child, every band must be present in either the dad or mom.

If a child has a band that neither parent has, then that child is not biologically related.

Look at Child 5:
- One band near the top (large fragment) is not present in either parent.
- That means this child cannot have inherited that DNA from either parent → impossible unless mutation (but rare).

Other children:
- Child 1–4 and 6: All bands match either mom or dad.

✔ Child 5 has an extra band → not biologically related.

> ✔️ Answer: Child 5

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## ✔ Summary of Answers:

| Question | Answer |
|--------|--------|
| Who is Jessica’s father? | Dad 2 |
| Who is the murderer? | S1 |
| Who raped Suzy? | S1 |
| Which child is not biologically related? | Child 5 |

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## 🧠 Key Concepts Recap:

- DNA fingerprinting uses restriction enzyme digestion + gel electrophoresis.
- Band patterns are unique to individuals.
- In paternity tests, a child’s bands must be present in either parent.
- In forensics, the suspect must have identical banding pattern to the evidence.

Let me know if you'd like a visual explanation or want to go over any part in detail!