Pedigree Practice Worksheet | PDF | Zygosity | Dominance (Genetics) - Free Printable

Problem Analysis and Solution

The image contains three pedigree charts, each representing a different genetic condition: Huntington's Disease, Hitchhiker's Thumb, and Colorblindness. Below is a detailed explanation and solution for each part of the worksheet.

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#### Pedigree 1: Huntington's Disease

1. Which members of the family above are afflicted with Huntington’s Disease?
- Affected individuals are represented by black symbols.
- 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?
- Individuals I-1 and I-2 have 4 children: II-1, II-2, II-3, II-4.

4. How many girls did II-1 and II-2 have? How many of these daughters have Huntington’s Disease?
- II-1 and II-2 have 2 daughters: III-2 and III-3.
- Only one daughter (III-3) 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 son of I-1 and I-2. Therefore, III-2 and II-4 are first cousins.
- I-2 and III-5: I-2 is the mother of II-4 and II-5, and III-5 is the son of II-4 and II-5. Therefore, I-2 is the grandmother of III-5.

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#### 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 are affected. This suggests it is a recessive trait.

7. How do you know?
- In generation III, individual III-4 is affected, and her parents (II-3 and II-4) are unaffected. For a recessive trait, both parents must be carriers to produce an affected offspring.

8. How are individuals III-2 and III-3 related?
- III-2 and III-3 are siblings, as they share the same parents (II-1 and II-2).

9. How would you name the 2 individuals that have hitchhiker’s thumb?
- The two individuals with hitchhiker’s thumb are III-4 and IV-2.

10. Name the 2 individuals that were carriers of hitchhiker’s thumb.
- Carriers are individuals who are heterozygous for the recessive trait. Possible carriers include:
- II-3 and II-4 (parents of III-4).
- II-5 and II-6 (parents of IV-2 and IV-4).

11. Is it possible for individual IV-3 to be a carrier? Why?
- Yes, it is possible. IV-3’s parents (III-4 and III-5) are heterozygous carriers (since III-4 is affected and III-5 is unaffected but could be a carrier). Therefore, IV-3 could inherit one recessive allele and be a carrier.

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#### Pedigree 3: Colorblindness

12. Which sex can be carriers of colorblindness and not have it?
- Females can be carriers of colorblindness without being affected because they have two X chromosomes. If one X chromosome carries the normal allele and the other carries the mutated allele, they will not express the trait but will be carriers.

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 inherited the mutated X chromosome from his mother (III-6). Since males have only one X chromosome, if it carries the mutated allele, they will express the trait.

15. Why do all the daughters in generation II carry the colorblind gene?
- All daughters in generation II inherited the mutated X chromosome from their father (I-1), who is colorblind. Since females have two X chromosomes, they will be carriers but not affected unless they inherit two mutated alleles.

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

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Final Answers

1. Afflicted members: I-1, II-2, II-3, II-7, III-3.
2. Dominant trait.
3. 4 children.
4. 2 daughters; 1 daughter has Huntington’s Disease.
5. III-2 and II-4: first cousins; I-2 and III-5: grandmother and grandson.
6. Recessive trait.
7. Affected offspring from unaffected parents.
8. Siblings.
9. III-4 and IV-2.
10. II-3, II-4, II-5, II-6.
11. Yes, possible; IV-3’s parents are carriers.
12. Females.
13. X-linked recessive trait.
14. Inherited mutated X chromosome from mother.
15. Inherited mutated X chromosome from father.
16. IV-1 and IV-7.

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Final Boxed Answers

\[
\boxed{
\begin{array}{l}
1. \text{I-1, II-2, II-3, II-7, III-3} \\
2. \text{Dominant} \\
3. 4 \\
4. 2, 1 \\
5. \text{First cousins; grandmother and grandson} \\
6. \text{Recessive} \\
7. \text{Affected offspring from unaffected parents} \\
8. \text{Siblings} \\
9. \text{III-4 and IV-2} \\
10. \text{II-3, II-4, II-5, II-6} \\
11. \text{Yes, possible; IV-3’s parents are carriers} \\
12. \text{Females} \\
13. \text{X-linked recessive} \\
14. \text{Inherited mutated X chromosome from mother} \\
15. \text{Inherited mutated X chromosome from father} \\
16. \text{IV-1 and IV-7}
\end{array}
}
\]