Lab Analysis
Learning Objectives
In this lesson, you will practice analyzing experimental data related to genetics, including interpreting pedigrees, gel electrophoresis results, and genetic cross data.
- Interpret pedigree charts to determine inheritance patterns
- Analyze gel electrophoresis results for DNA fingerprinting
- Use chi-square analysis to evaluate genetic cross results
- Draw conclusions from experimental genetics data
Sample Lab Scenario
Experiment: Testing Mendel's Law of Segregation
Background: A student crossed heterozygous tall pea plants (Tt x Tt) and counted the offspring phenotypes.
| Phenotype | Expected Ratio | Expected Number (out of 200) | Observed Number |
|---|---|---|---|
| Tall | 3/4 | 150 | 145 |
| Short | 1/4 | 50 | 55 |
Analysis Questions to Consider:
- Do the observed results match the expected 3:1 ratio?
- What factors might cause deviation from expected results?
- Is this deviation statistically significant?
Practice Quiz
Test your lab analysis skills with these 10 questions. Click on each question to reveal the answer.
1. In the pea plant experiment above, why might the observed numbers differ from expected numbers?
Answer: Random chance during fertilization, small sample size, environmental factors affecting survival, or experimental error in counting. These small deviations are normal and expected in real experiments.
2. A pedigree shows that an affected father and carrier mother have children. All daughters are carriers and all sons are affected. What type of inheritance is this?
Answer: X-linked recessive inheritance. The trait passes from affected father to carrier daughters (who receive his X chromosome), and carrier mothers can pass the affected X to sons (who only have one X).
3. In gel electrophoresis, smaller DNA fragments move _____ through the gel and appear _____ to the bottom.
Answer: Smaller DNA fragments move FASTER through the gel and appear CLOSER to the bottom. This is because smaller fragments can move more easily through the pores in the gel matrix.
4. A corn plant cross produces 720 purple kernels and 240 yellow kernels. Does this fit a 3:1 ratio?
Answer: Yes, it perfectly fits a 3:1 ratio. Total = 960 kernels. Expected 3:1 would be 720 purple : 240 yellow. The observed matches the expected exactly.
5. Why is gel electrophoresis useful in genetic testing?
Answer: Gel electrophoresis separates DNA fragments by size, allowing scientists to compare DNA samples, identify mutations, determine genetic relationships (DNA fingerprinting), and analyze gene expression patterns.
6. In a pedigree, a trait appears in every generation and affects both males and females equally. What type of inheritance is most likely?
Answer: Autosomal dominant inheritance. Dominant traits appear in every generation when passed from an affected parent, and autosomal means it's not sex-linked, so both sexes are equally affected.
7. A scientist observes 9:3:3:1 ratio in a dihybrid cross instead of the expected ratio. The actual numbers are 315:108:101:32. Calculate if this matches the expected ratio for 556 total offspring.
Answer: Expected for 556 offspring in 9:3:3:1: 312.75 : 104.25 : 104.25 : 34.75. The observed (315:108:101:32) is very close to expected, showing good agreement with Mendel's predicted ratio.
8. A DNA sample shows bands at positions that match both the mother's and father's bands. What can you conclude?
Answer: This is consistent with the sample being from a biological child of these parents. Each child inherits half their DNA from each parent, so their DNA fingerprint should show bands from both parents.
9. Why do geneticists often use organisms like fruit flies or pea plants for genetic experiments?
Answer: These organisms have short generation times (allowing quick observation of inheritance), produce many offspring (providing large sample sizes), have easily observable traits, are easy to care for, and have well-understood genetics.
10. A pedigree shows two unaffected parents with an affected child. What does this indicate about the inheritance pattern?
Answer: This indicates autosomal recessive inheritance. Both parents must be carriers (heterozygous) for the recessive allele. When two carriers have children, there's a 25% chance of having an affected (homozygous recessive) child.
Next Steps
- Practice interpreting more pedigrees
- Continue to the Claim-Evidence Writing lesson
- Review gel electrophoresis concepts