Solved Pedigree Worksheet I ho = Huntingtons Disease II 2 4 ... - Free Printable

Let’s go step by step through each question using the pedigree chart.

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1. Which members of the family above are afflicted with Huntington’s Disease?

Look at the legend: black square or circle = has Huntington’s Disease.

Go generation by generation:

- Generation I: Individual I-1 (black square) → has it.
- Generation II: Individuals II-2 (black circle), II-3 (black square), II-7 (black circle) → have it.
- Generation III: Individual III-3 (black circle) → has it.

So, list them:
→ I-1, II-2, II-3, 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 what “dominant” means.

Also, look at the pedigree: affected people (like I-1) have children who are NOT affected (like II-4, II-5, II-6, II-8). If it were recessive, both parents would need to carry it to pass it on — but here, an affected parent can have unaffected kids, which fits dominant inheritance (because the unaffected kids just didn’t inherit the dominant allele).

So → Dominant

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3. How many children did individuals I-1 and I-2 have?

Look at Generation II — all the kids connected to I-1 and I-2.

They are: II-1, II-2, II-3, II-4, II-5, II-6, II-7, II-8 → that’s 8 children.

Wait — actually, II-1 is married into the family (he’s a spouse, not a child of I-1/I-2). Let’s check the lines.

In pedigrees, horizontal line between two people = they are partners. Vertical line down from them = their children.

I-1 and I-2 are connected by a horizontal line. From that line, vertical lines go down to: II-2, II-3, II-4, II-5, II-6, II-7, II-8 → that’s 7 children.

II-1 is married to II-2 — so he’s not their child.

So → 7 children

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

II-1 (square = male) and II-2 (circle = female, affected) are partners.

Their children are in Generation III: III-1, III-2, III-3.

Circles = girls → III-2 and III-3 → that’s 2 girls.

Which of those have Huntington’s? Look at shading: III-3 is black → has it. III-2 is white → does not.

So → 2 girls, 1 has Huntington’s

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5. How are individuals III-2 and II-4 related? I-2 and III-5?

First: III-2 and II-4

III-2 is daughter of II-2 and II-1.

II-4 is son of I-1 and I-2 → so II-4 is brother of II-2.

That makes II-4 the uncle of III-2.

So → Uncle and niece

Second: I-2 and III-5

I-2 is grandmother (mother of II-4 and II-5).

III-5 is child of II-4 and II-5 → so III-5 is grandchild of I-2.

So → Grandmother and grandson

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Final Answer:

1. I-1, II-2, II-3, II-7, III-3
2. Dominant
3. 7
4. 2 girls; 1 has Huntington’s Disease
5. Uncle and niece; Grandmother and grandson