Pedigree Worksheet & KEY - Free Printable

Problem Analysis and Solution

The worksheet involves analyzing three different pedigrees to determine the inheritance patterns of genetic traits: Huntington's Disease, Hitchhiker's Thumb, and Colorblindness. Let's solve each part step by step.

---

#### Pedigree 1: Huntington's Disease

1. Which members of the family above are afflicted with Huntington’s Disease?
- Affected individuals are represented by black-filled circles or squares.
- Afflicted members: I-1, II-2, II-3, II-7, III-3.

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?
- Since there are no carriers (only affected or unaffected individuals), and the disease skips generations, it is caused by a dominant trait.

3. How many children did individuals I-1 and I-2 have?
- Count the number of offspring in generation II.
- They have 8 children: II-1, II-2, II-3, II-4, II-5, II-6, II-7, II-8.

4. How many girls did II-1 and II-2 have? How many have Huntington’s Disease?
- II-1 and II-2 have 2 children: III-1 (boy) and III-2 (girl).
- Neither child has Huntington’s Disease.

5. How are individuals III-2 and II-4 related? I-2 and III-5?
- III-2 and II-4: III-2 is the daughter of II-1 and II-2, and II-4 is the daughter of II-4 and II-5. They are first cousins.
- I-2 and III-5: I-2 is the grandmother of III-5. They are grandmother-grandson.

---

#### Pedigree 2: Hitchhiker’s Thumb

6. Is this trait dominant or recessive?
- The trait appears in multiple generations but not all offspring of affected parents have the trait. This suggests it is recessive.

7. How do you know?
- In generation IV, both IV-1 and IV-3 have the trait (filled circles). Their parents (III-1 and III-2) do not have the trait, indicating that the parents are heterozygous carriers. This pattern is consistent with a recessive trait.

8. How are individuals III-1 and III-2 related?
- III-1 and III-2 are siblings (brother and sister).

9. How would you name the 2 individuals that have hitchhiker’s thumb?
- Individuals with hitchhiker’s thumb: IV-1 and IV-3.

10. Name the 2 individuals that were carriers of hitchhiker’s thumb.
- Carriers are individuals who do not express the trait but can pass it on. These are likely III-1 and III-2, as they are the parents of IV-1 and IV-3.

11. Is it possible for individual IV-2 to be a carrier? Why?
- Yes, it is possible. IV-2 is the sibling of IV-1 and IV-3, who both have the recessive trait. Therefore, IV-2 could be a carrier (heterozygous) since their parents (III-1 and III-2) must both be carriers.

---

#### Pedigree 3: Colorblindness

12. Which sex can be carriers of colorblindness and not have it?
- Females can be carriers of colorblindness (X-linked recessive trait) without expressing the trait because they have two X chromosomes. Males, having only one X chromosome, will express the trait if they inherit the mutated gene.

13. With this in mind, what kind of trait is colorblindness (use your notes)?
- Colorblindness is an X-linked recessive trait.

14. Why does individual IV-7 have colorblindness?
- IV-7 is male and has inherited the mutated X chromosome from his mother (III-5). Since males have only one X chromosome, they will express the trait if it is present.

15. Why do all the daughters in generation II carry the colorblind gene?
- All daughters in generation II carry the colorblind gene because their father (I-1) is colorblind (homozygous for the recessive allele). He passes his X chromosome (with the mutated gene) to all his daughters.

16. Name 2 IV generation colorblind males.
- IV-1 and IV-7 are colorblind males.

---

Final Answers

1. Afflicted members: I-1, II-2, II-3, II-7, III-3
2. Dominant trait
3. 8 children
4. 2 girls, 0 with Huntington’s Disease
5. III-2 and II-4: first cousins; I-2 and III-5: grandmother-grandson
6. Recessive trait
7. Pattern of inheritance shows non-expression in heterozygotes
8. Siblings
9. IV-1 and IV-3
10. III-1 and III-2
11. Yes, IV-2 could be a carrier because her parents are carriers
12. Females
13. X-linked recessive trait
14. IV-7 inherited the mutated X chromosome from his mother
15. All daughters inherited the mutated X chromosome from their colorblind father
16. IV-1 and IV-7

---

Final Boxed Answers:

1. I-1, II-2, II-3, II-7, III-3
2. Dominant
3. 8
4. 2, 0
5. First cousins; Grandmother-grandson
6. Recessive
7. Pattern of inheritance shows non-expression in heterozygotes
8. Siblings
9. IV-1 and IV-3
10. III-1 and III-2
11. Yes, because her parents are carriers
12. Females
13. X-linked recessive
14. Inherited the mutated X chromosome from his mother
15. All daughters inherited the mutated X chromosome from their colorblind father
16. IV-1 and IV-7

Final Answer: \boxed{See detailed solutions above}