Pedigree Worksheet - Free Printable

Let's solve the Pedigree Worksheet step by step, based on the information provided in the image.

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Part 1: Huntington’s Disease Pedigree

We are given a pedigree for Huntington’s Disease, where:
- Red squares (♂) and red circles (♀) = affected
- White squares and circles = unaffected
- No carriers — either you have it or you don’t.

#### Question 1: Which members of the family above are afflicted with Huntington’s Disease?

Looking at the first pedigree:

- I-1 (male, red square) → Affected
- II-1 (female, red circle) → Affected
- II-2 (male, red square) → Affected
- II-5 (female, red circle) → Affected
- II-6 (female, red circle) → Affected
- III-1 (male, red square) → Affected
- III-3 (female, red circle) → Affected

So, the affected individuals are:
> I-1, II-1, II-2, II-5, II-6, III-1, III-3

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#### Question 2: Is Huntington’s Disease caused by a dominant or recessive trait?

We are told: There are no carriers — you either have it or you don't. This is a key clue.

Also, observe:
- I-1 has the disease.
- I-1 and I-2 (unaffected) have children.
- Some children (II-1, II-2, II-5, II-6) have the disease.
- But I-2 is unaffected, so she cannot pass on the disease allele if it were recessive (because then both parents would need to be carriers).
- However, since some children are affected and one parent is affected, and the other is not, this suggests that the disease is dominant.

In dominant inheritance:
- Only one copy of the mutant allele is needed to express the disease.
- An affected individual (I-1) can pass it to offspring even if the other parent is unaffected.

Thus:
> Dominant trait

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#### Question 3: How many children did individuals I-1 and I-2 have?

Look at generation II: They have 6 children: II-1 through II-6.

> 6 children

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#### Question 4: How many girls did II-1 and II-2 have? How many have Huntington’s Disease?

II-1 and II-2 are a couple in generation II.

From the pedigree:
- II-1 is female (circle), II-2 is male (square)
- Their children are in generation III: III-1, III-2, III-3

So:
- III-1 = male (square)
- III-2 = female (circle)
- III-3 = female (circle)

So they had 2 girls: III-2 and III-3

Now, who has Huntington’s?
- III-2: white circle → unaffected
- III-3: red circle → affected

So:
> They had 2 girls; 1 has Huntington’s Disease

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#### Question 5: How is individual III-2 related to II-4 and III-5?

First, identify:
- III-2: daughter of II-1 and II-2
- II-4: son of I-1 and I-2 (same as II-1 and II-2’s parent)
- III-5: child of II-4 and II-5

So:
- II-4 and II-5 are parents of III-5
- II-1 and II-2 are siblings of II-4 and II-5? Wait — let's check:

II-1 and II-2 are children of I-1 and I-2
II-4 and II-5 are also children of I-1 and I-2 → so II-1, II-2, II-4, II-5 are all siblings

Therefore:
- III-2 is daughter of II-1 and II-2
- III-5 is child of II-4 and II-5

So:
- III-2 and III-5 are cousins (children of siblings)

But the question asks: How is III-2 related to II-4 and III-5?

- III-2 and II-4: II-4 is the uncle of III-2 (since II-4 is sibling of III-2’s parent, II-1 or II-2)
- III-2 and III-5: first cousins

Answer:
> II-4 is the uncle of III-2; III-5 is the cousin of III-2

Or more precisely:
> III-2 is the niece of II-4; III-5 is the cousin of III-2

But likely expecting:
> III-2 is the niece of II-4 and the cousin of III-5

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Part 2: Hitchhiker’s Thumb Pedigree

Now we analyze the second pedigree for Hitchhiker’s Thumb.

Note: Carriers are intentionally not shown — meaning if someone has the trait, they show it; if not, they’re normal.

#### Question 6: Is this trait dominant or recessive?

Look at the pedigree:

- I-1 and I-2: both normal (white)
- They have a child (II-1) who has hitchhiker’s thumb (red)

This means:
- Both parents are normal but have an affected child
- So the trait must be recessive — because both parents must carry the recessive allele to pass it on.

If it were dominant, at least one parent would have to show the trait.

> Recessive trait

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#### Question 7: How do you know?

Because two unaffected parents (I-1 and I-2) produced an affected child (II-1). This only happens in recessive traits when both parents are carriers.

> Two unaffected parents had an affected child, which is only possible if the trait is recessive.

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#### Question 8: How are individuals III-1 and II-2 related?

Check the pedigree:

- II-2 is a female in generation II
- III-1 is a male in generation III
- II-2’s children: III-1 and III-2

So:
> III-1 is the son of II-2

Thus:
> III-1 is the child of II-2

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#### Question 9: Name 2 individuals that have hitchhiker’s thumb.

Look at the red symbols:
- II-1 (male)
- IV-2 (female)
- IV-3 (female)

Any two:
> II-1 and IV-2 (or IV-3)

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#### Question 10: Name 2 individuals that were carriers of hitchhiker’s thumb.

Since the trait is recessive, carriers are heterozygous and do not show the trait (they are white).

We need to find individuals who are unaffected but must carry the recessive allele because they had an affected child.

Look at:
- II-2: She is unaffected, but her child III-1 is affected (has hitchhiker’s thumb)
→ So II-2 must be a carrier

- II-3: Unaffected, but her child IV-2 is affected → so II-3 is a carrier

- II-4: Unaffected, but child IV-3 is affected → so II-4 is a carrier

So any two:
> II-2 and II-3 (or II-4)

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#### Question 11: Is it possible for individual IV-2 to be a carrier? Why?

IV-2 has the trait (red circle), so she shows the recessive phenotype.

That means she is homozygous recessive (aa) — she has two copies of the recessive allele.

She cannot be a carrier in the traditional sense — because carriers are heterozygous (Aa) and don’t show the trait.

But since IV-2 shows the trait, she is not a carrier — she is affected.

> No, because IV-2 has the trait, so she is homozygous recessive (aa). Carriers are heterozygous and do not show the trait.

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✔ Final Answers:

#### Huntington’s Disease Questions:

1. Affected individuals: I-1, II-1, II-2, II-5, II-6, III-1, III-3
2. Dominant – because affected individuals have affected children even when one parent is unaffected, and there are no carriers.
3. 6 children
4. 2 girls; 1 has Huntington’s Disease
5. III-2 is the niece of II-4 and the cousin of III-5

#### Hitchhiker’s Thumb Questions:

6. Recessive
7. Because two unaffected parents had an affected child (II-1), which is only possible with a recessive trait.
8. III-1 is the child of II-2
9. II-1 and IV-2 (or IV-3)
10. II-2 and II-3 (or II-4)
11. No, because IV-2 has the trait, meaning she is homozygous recessive (aa); carriers are heterozygous and do not express the trait.

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