Pedigree worksheet illustrating inheritance patterns of Huntington's Disease with questions about affected individuals, carrier status, and genetic traits.
Pedigree worksheet showing a family tree with symbols indicating Huntington's Disease, including affected individuals, carriers, and relationships across generations.
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Show Answer Key & Explanations
Step-by-step solution for: Pedigree Worksheet
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Show Answer Key & Explanations
Step-by-step solution for: Pedigree Worksheet
Let’s go through each question step by step. We’ll use the pedigree chart to find answers based on who is shaded (has Huntington’s) and who isn’t.
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1. Which members of the family above are afflicted with Huntington's Disease?
Look at the key:
- Red square or circle = has Huntington’s
- White square or circle = no disease
In generation I: Individual 1 (red square) → has it
Generation II: Individuals 2, 3, 6, 7 (all red) → have it
Generation III: Individual 3 (red circle) → has it
So list them:
I-1, II-2, II-3, II-6, II-7, III-3
✔ Answer: I-1, II-2, II-3, II-6, II-7, III-3
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2. There are no carriers for Huntington's Disease - you either have it or you don't. With this in mind, is Huntington's disease caused by a dominant or recessive trait?
If there are NO carriers, that means if you have even one copy of the gene, you show the disease. That’s how dominant traits work.
Recessive traits need two copies — and people with one copy are “carriers” but don’t show symptoms. But here, no carriers exist → so it must be dominant.
✔ Answer: Dominant
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3. How many children did individuals I-1 and I-2 have?
Count all the lines going down from I-1 and I-2 to generation II.
They have 8 children: II-1 through II-8.
✔ Answer: 8
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4. How many girls did II-1 and II-2 have? _________ How many have Huntington's Disease? _________
II-1 (white square) and II-2 (red circle) have 3 children in generation III: III-1 (boy), III-2 (girl), III-3 (girl).
Girls: III-2 and III-3 → 2 girls
Which of those girls have Huntington’s? Only III-3 is red → 1 girl has it.
✔ Answer: 2 girls; 1 has Huntington’s
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5. How is individual III-2 and II-4 related? _______________ I-2 and III-5? _______________
III-2 is child of II-1 and II-2.
II-4 is sibling of II-2 → so II-4 is aunt/uncle of III-2.
Since II-4 is male (square), he’s the uncle of III-2.
Now, I-2 is parent of II-4, and II-4 is parent of III-5 → so I-2 is grandparent of III-5.
✔ Answer: Uncle and niece; Grandmother and grandson
*(Note: III-5 is male — white square — so grandson)*
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6. The pedigree to the right shows the passing on of Hitchhiker’s Thumb in a family. Is this trait dominant or recessive?
Key clue: “Carriers are intentionally not shown.” So if someone doesn’t have the trait, they’re NOT a carrier — meaning they have zero copies of the gene.
Also, look at IV-1 and IV-3 — they have hitchhiker’s thumb (shaded). Their parents (III-1 and III-2) do NOT have it.
That means two unaffected parents had affected children → which can ONLY happen if the trait is recessive.
Because for recessive traits, both parents can carry the gene without showing it — but wait! The note says “carriers are intentionally not shown.” Hmm… actually, let’s think again.
Wait — if carriers are NOT shown, then anyone who doesn’t have the trait has NO copies. So if two people without the trait have a child WITH the trait, that would be impossible unless... unless the trait is recessive AND carriers ARE being hidden? But the note says carriers are NOT shown — meaning we assume non-shaded = no gene at all.
But in reality, for recessive traits, you NEED two carriers to make an affected child. If carriers aren’t shown, then the only way this makes sense is if the trait is recessive, and the diagram is hiding carriers — but the problem says “carriers are intentionally not shown,” which implies that when someone is unshaded, they might still be a carrier — but we just don’t mark them.
Actually, let’s re-read: “Carriers are intentionally not shown in this pedigree.” That probably means that carriers exist but are drawn as normal (unshaded). So if two unshaded people have a shaded child, that proves the trait is recessive — because both parents must be carriers (even though not marked).
Yes — classic sign of recessive inheritance: unaffected parents → affected child.
✔ Answer: Recessive
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7. How do you know?
Because individuals III-1 and III-2 do not have hitchhiker’s thumb (they’re unshaded), but their children IV-1 and IV-3 DO have it. For that to happen, both parents must carry the recessive allele — even though they don’t show the trait. That’s only possible if the trait is recessive.
✔ Answer: Two unaffected parents (III-1 and III-2) have affected children (IV-1 and IV-3), which only happens with recessive traits.
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8. How are individuals III-1 and III-2 related?
Look at the chart: They are married (connected by horizontal line) and have children together → they are spouses or married couple.
✔ Answer: They are married / spouses
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9. Name 2 individuals that have hitchhiker’s thumb.
Shaded symbols = have the trait.
IV-1 (red square), IV-3 (red circle)
Also, maybe others? Let’s check:
Generation IV: IV-1 and IV-3 are shaded.
Any others? No — only those two are shaded in the whole second pedigree.
Wait — what about earlier generations? All others are unshaded.
So yes: IV-1 and IV-3
✔ Answer: IV-1 and IV-3
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10. Name 2 individuals that were carriers of hitchhiker’s thumb.
Carriers = have one copy of the recessive gene but don’t show the trait.
We know III-1 and III-2 must be carriers because they have affected children (IV-1 and IV-3) but don’t show the trait themselves.
Also, possibly others? Like II-1 and II-2? Not necessarily — we don’t have enough info. But III-1 and III-2 are definite carriers.
The question asks for 2 — so pick III-1 and III-2.
✔ Answer: III-1 and III-2
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11. Is it possible for individual IV-2 to be a carrier? Why?
IV-2 is unshaded → does not have hitchhiker’s thumb.
Her parents are III-1 and III-2 — both carriers (as established).
When two carriers have a child, the chances are:
- 25% chance child has trait (homozygous recessive)
- 50% chance child is carrier (heterozygous)
- 25% chance child has no gene (homozygous dominant)
IV-2 does not have the trait → so she could be either homozygous dominant OR heterozygous (carrier).
So YES — it’s possible she’s a carrier.
✔ Answer: Yes, because her parents are both carriers, so she could have inherited one recessive allele and one dominant allele — making her a carrier without showing the trait.
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Final Answer:
1. I-1, II-2, II-3, II-6, II-7, III-3
2. Dominant
3. 8
4. 2 girls; 1 has Huntington’s
5. Uncle and niece; Grandmother and grandson
6. Recessive
7. Two unaffected parents (III-1 and III-2) have affected children (IV-1 and IV-3), which only happens with recessive traits.
8. Spouses / Married couple
9. IV-1 and IV-3
10. III-1 and III-2
11. Yes, because her parents are both carriers, so she could have inherited one recessive allele and one dominant allele — making her a carrier without showing the trait.
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1. Which members of the family above are afflicted with Huntington's Disease?
Look at the key:
- Red square or circle = has Huntington’s
- White square or circle = no disease
In generation I: Individual 1 (red square) → has it
Generation II: Individuals 2, 3, 6, 7 (all red) → have it
Generation III: Individual 3 (red circle) → has it
So list them:
I-1, II-2, II-3, II-6, II-7, III-3
✔ Answer: I-1, II-2, II-3, II-6, II-7, III-3
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2. There are no carriers for Huntington's Disease - you either have it or you don't. With this in mind, is Huntington's disease caused by a dominant or recessive trait?
If there are NO carriers, that means if you have even one copy of the gene, you show the disease. That’s how dominant traits work.
Recessive traits need two copies — and people with one copy are “carriers” but don’t show symptoms. But here, no carriers exist → so it must be dominant.
✔ Answer: Dominant
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3. How many children did individuals I-1 and I-2 have?
Count all the lines going down from I-1 and I-2 to generation II.
They have 8 children: II-1 through II-8.
✔ Answer: 8
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4. How many girls did II-1 and II-2 have? _________ How many have Huntington's Disease? _________
II-1 (white square) and II-2 (red circle) have 3 children in generation III: III-1 (boy), III-2 (girl), III-3 (girl).
Girls: III-2 and III-3 → 2 girls
Which of those girls have Huntington’s? Only III-3 is red → 1 girl has it.
✔ Answer: 2 girls; 1 has Huntington’s
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5. How is individual III-2 and II-4 related? _______________ I-2 and III-5? _______________
III-2 is child of II-1 and II-2.
II-4 is sibling of II-2 → so II-4 is aunt/uncle of III-2.
Since II-4 is male (square), he’s the uncle of III-2.
Now, I-2 is parent of II-4, and II-4 is parent of III-5 → so I-2 is grandparent of III-5.
✔ Answer: Uncle and niece; Grandmother and grandson
*(Note: III-5 is male — white square — so grandson)*
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6. The pedigree to the right shows the passing on of Hitchhiker’s Thumb in a family. Is this trait dominant or recessive?
Key clue: “Carriers are intentionally not shown.” So if someone doesn’t have the trait, they’re NOT a carrier — meaning they have zero copies of the gene.
Also, look at IV-1 and IV-3 — they have hitchhiker’s thumb (shaded). Their parents (III-1 and III-2) do NOT have it.
That means two unaffected parents had affected children → which can ONLY happen if the trait is recessive.
Because for recessive traits, both parents can carry the gene without showing it — but wait! The note says “carriers are intentionally not shown.” Hmm… actually, let’s think again.
Wait — if carriers are NOT shown, then anyone who doesn’t have the trait has NO copies. So if two people without the trait have a child WITH the trait, that would be impossible unless... unless the trait is recessive AND carriers ARE being hidden? But the note says carriers are NOT shown — meaning we assume non-shaded = no gene at all.
But in reality, for recessive traits, you NEED two carriers to make an affected child. If carriers aren’t shown, then the only way this makes sense is if the trait is recessive, and the diagram is hiding carriers — but the problem says “carriers are intentionally not shown,” which implies that when someone is unshaded, they might still be a carrier — but we just don’t mark them.
Actually, let’s re-read: “Carriers are intentionally not shown in this pedigree.” That probably means that carriers exist but are drawn as normal (unshaded). So if two unshaded people have a shaded child, that proves the trait is recessive — because both parents must be carriers (even though not marked).
Yes — classic sign of recessive inheritance: unaffected parents → affected child.
✔ Answer: Recessive
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7. How do you know?
Because individuals III-1 and III-2 do not have hitchhiker’s thumb (they’re unshaded), but their children IV-1 and IV-3 DO have it. For that to happen, both parents must carry the recessive allele — even though they don’t show the trait. That’s only possible if the trait is recessive.
✔ Answer: Two unaffected parents (III-1 and III-2) have affected children (IV-1 and IV-3), which only happens with recessive traits.
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8. How are individuals III-1 and III-2 related?
Look at the chart: They are married (connected by horizontal line) and have children together → they are spouses or married couple.
✔ Answer: They are married / spouses
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9. Name 2 individuals that have hitchhiker’s thumb.
Shaded symbols = have the trait.
IV-1 (red square), IV-3 (red circle)
Also, maybe others? Let’s check:
Generation IV: IV-1 and IV-3 are shaded.
Any others? No — only those two are shaded in the whole second pedigree.
Wait — what about earlier generations? All others are unshaded.
So yes: IV-1 and IV-3
✔ Answer: IV-1 and IV-3
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10. Name 2 individuals that were carriers of hitchhiker’s thumb.
Carriers = have one copy of the recessive gene but don’t show the trait.
We know III-1 and III-2 must be carriers because they have affected children (IV-1 and IV-3) but don’t show the trait themselves.
Also, possibly others? Like II-1 and II-2? Not necessarily — we don’t have enough info. But III-1 and III-2 are definite carriers.
The question asks for 2 — so pick III-1 and III-2.
✔ Answer: III-1 and III-2
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11. Is it possible for individual IV-2 to be a carrier? Why?
IV-2 is unshaded → does not have hitchhiker’s thumb.
Her parents are III-1 and III-2 — both carriers (as established).
When two carriers have a child, the chances are:
- 25% chance child has trait (homozygous recessive)
- 50% chance child is carrier (heterozygous)
- 25% chance child has no gene (homozygous dominant)
IV-2 does not have the trait → so she could be either homozygous dominant OR heterozygous (carrier).
So YES — it’s possible she’s a carrier.
✔ Answer: Yes, because her parents are both carriers, so she could have inherited one recessive allele and one dominant allele — making her a carrier without showing the trait.
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Final Answer:
1. I-1, II-2, II-3, II-6, II-7, III-3
2. Dominant
3. 8
4. 2 girls; 1 has Huntington’s
5. Uncle and niece; Grandmother and grandson
6. Recessive
7. Two unaffected parents (III-1 and III-2) have affected children (IV-1 and IV-3), which only happens with recessive traits.
8. Spouses / Married couple
9. IV-1 and IV-3
10. III-1 and III-2
11. Yes, because her parents are both carriers, so she could have inherited one recessive allele and one dominant allele — making her a carrier without showing the trait.
Parent Tip: Review the logic above to help your child master the concept of pedigrees worksheet.
