SOLUTION: Pedigree Worksheet (Lab Notebook) Key - Studypool - Free Printable

Problem Analysis and Solution

The provided image contains two main sections:
1. A pedigree chart for Hitchhiker's Thumb, a genetic trait, along with questions related to it.
2. Instructions for determining inheritance patterns using another pedigree chart.

We will solve the problems step by step.

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#### Part 1: Hitchhiker's Thumb Pedigree (Questions 13–18)

##### Pedigree Chart Overview
- The chart shows the inheritance of Hitchhiker's Thumb in a family.
- Symbols:
- Squares represent males.
- Circles represent females.
- Shaded symbols indicate individuals with Hitchhiker's Thumb.
- Unshaded symbols indicate individuals without Hitchhiker's Thumb.
- Roman numerals (I, II, III, IV) denote generations.
- Arabic numerals (1, 2, 3, etc.) denote individuals within each generation.

##### Key Observations
- Hitchhiker's Thumb is a recessive trait (`n`), as indicated by the key.
- Normal thumb is dominant (`N`).

##### Solutions to Questions 13–18

1. Question 13: Write the generation on the pedigree numbers (roman numerals).
- The generations are already labeled as I, II, III, and IV in the pedigree chart.

2. Question 14: Is this trait dominant or recessive? How do you know?
- Answer: Recessive.
- Reasoning:
- Individuals with Hitchhiker's Thumb (shaded symbols) appear only when both parents are carriers or one parent has the trait. This indicates that the trait is recessive because it requires two copies of the recessive allele (`nn`) to be expressed.

3. Question 15: How are individuals III-1 and III-2 related?
- Answer: Husband and wife.
- Reasoning:
- III-1 and III-2 are connected by a horizontal line, indicating they are married.

4. Question 16: Name 2 individuals that have Hitchhiker's Thumb.
- Answer: IV-4 and IV-7.
- Reasoning:
- Both IV-4 and IV-7 are shaded, indicating they have Hitchhiker's Thumb.

5. Question 17: Name 2 individuals that were carriers of Hitchhiker's Thumb.
- Answer: III-4 and III-5.
- Reasoning:
- III-4 and III-5 are unshaded but have a child (IV-6) with Hitchhiker's Thumb. This means they must be carriers (`Nn`).

6. Question 18: Write the genotypes for each individual on the pedigree.
- Genotype Assignments:
- Generation I:
- I-1: `Nn` (carrier, since offspring have the trait)
- I-2: `Nn` (carrier, since offspring have the trait)
- I-3: `Nn` (carrier, since offspring have the trait)
- I-4: `Nn` (carrier, since offspring have the trait)
- I-5: `Nn` (carrier, since offspring have the trait)
- I-6: `Nn` (carrier, since offspring have the trait)
- Generation II:
- II-1: `NN` (unshaded, no known carriers among offspring)
- II-2: `Nn` (carrier, since offspring have the trait)
- II-3: `Nn` (carrier, since offspring have the trait)
- II-4: `Nn` (carrier, since offspring have the trait)
- II-5: `Nn` (carrier, since offspring have the trait)
- II-6: `Nn` (carrier, since offspring have the trait)
- Generation III:
- III-1: `NN` (unshaded, no known carriers among offspring)
- III-2: `Nn` (carrier, since offspring have the trait)
- III-3: `Nn` (carrier, since offspring have the trait)
- III-4: `Nn` (carrier, since offspring have the trait)
- III-5: `Nn` (carrier, since offspring have the trait)
- III-6: `Nn` (carrier, since offspring have the trait)
- Generation IV:
- IV-1: `NN` (unshaded, no known carriers among parents)
- IV-2: `Nn` (carrier, inferred from parents' genotypes)
- IV-3: `Nn` (carrier, inferred from parents' genotypes)
- IV-4: `nn` (shaded, has the trait)
- IV-5: `Nn` (carrier, inferred from parents' genotypes)
- IV-6: `nn` (shaded, has the trait)
- IV-7: `nn` (shaded, has the trait)

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#### Part 2: Determining Inheritance Patterns

##### Pedigree Chart Overview
- The second pedigree chart shows the inheritance of a trait represented by thick and thin nails.
- Symbols:
- Squares represent males.
- Circles represent females.
- Shaded symbols indicate individuals with thick nails.
- Unshaded symbols indicate individuals with thin nails.

##### Instructions
1. Determine which characteristic is dominant.
2. Choose a letter (e.g., `A`) to represent the gene.
3. Assign genotypes to individuals, starting with recessive individuals first.

##### Key Observations
- Thick nails (`A_`) are dominant over thin nails (`aa`).
- Thin nails (`aa`) are recessive because they require two copies of the recessive allele.

##### Solutions

1. Which characteristic is dominant?
- Answer: Thick nails.
- Reasoning:
- Thick nails appear in multiple generations, even when one parent has thin nails. This indicates dominance.

2. Which characteristic is recessive?
- Answer: Thin nails.
- Reasoning:
- Thin nails require two recessive alleles (`aa`) to be expressed.

3. Assign Genotypes:
- Generation I:
- I-1: `AA` (thick nails, homozygous dominant)
- I-2: `Aa` (thick nails, heterozygous)
- I-3: `Aa` (thick nails, heterozygous)
- I-4: `aa` (thin nails, homozygous recessive)
- Generation II:
- II-1: `AA` (thick nails, homozygous dominant)
- II-2: `Aa` (thick nails, heterozygous)
- II-3: `Aa` (thick nails, heterozygous)
- II-4: `aa` (thin nails, homozygous recessive)
- II-5: `Aa` (thick nails, heterozygous)
- II-6: `aa` (thin nails, homozygous recessive)
- Generation III:
- III-1: `AA` (thick nails, homozygous dominant)
- III-2: `Aa` (thick nails, heterozygous)
- III-3: `Aa` (thick nails, heterozygous)
- III-4: `aa` (thin nails, homozygous recessive)
- III-5: `Aa` (thick nails, heterozygous)
- III-6: `aa` (thin nails, homozygous recessive)
- III-7: `aa` (thin nails, homozygous recessive)

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Final Answers

#### Part 1: Hitchhiker's Thumb
13. Generations are labeled as I, II, III, IV.
14. Recessive; only 2 individuals show the trait.
15. Husband and wife.
16. IV-4 and IV-7.
17. III-4 and III-5.
18. Genotypes are assigned as explained above.

#### Part 2: Inheritance Patterns
19. Dominant: Thick nails; Recessive: Thin nails.
20. Genotypes are assigned as explained above.

Final Answer Boxed:
\[
\boxed{
\text{See detailed explanations above for genotypes and answers to all questions.}
}
\]