Question

Genetics Worksheet: Mutations, Frameshift, and Point Mutations
Passage:
Mutations are changes in the DNA sequence that can occur naturally during DNA replication or be caused by environmental factors such as radiation or chemicals. A point mutation occurs when a single nucleotide in the DNA sequence is changed, inserted, or deleted. Point mutations can result in silent, missense, or nonsense changes, depending on how they alter the resulting protein. Frameshift mutations occur when nucleotides are inserted or deleted from the DNA sequence in numbers not divisible by three. Because codons are read in groups of three, this shifts the reading frame and usually results in a completely different sequence of amino acids, often producing a nonfunctional protein.

Mutations are changes in the DNA sequence that can affect how genes function. There are several types of mutations: 1. **Point Mutation**: A change in a single nucleotide base. Example: Substitution of one base for another. 2. **Insertion**: Addition of one or more nucleotide bases into the DNA sequence. 3. **Deletion**: Removal of one or more nucleotide bases from the DNA sequence. 4. **Frameshift Mutation**: Caused by insertions or deletions that change the reading frame of the gene. 5. **Nonsense Mutation**: A point mutation that changes a codon into a stop codon, ending protein synthesis prematurely. 6. **Missense Mutation**: A point mutation that changes one amino acid in the protein sequence, possibly altering its function. 7. **Silent Mutation**: A mutation that does not change the amino acid sequence of the protein. These mutations can lead to genetic disorders or have no effect, depending on where they occur and how they alter protein function
Questions:
1. What is a mutation?
2. What causes point mutations?
3. How can a point mutation affect a protein?
4. What makes a frameshift mutation different from a point mutation?
5. Explain why frameshift mutations often lead to nonfunctional proteins.

Passage 1
Huntington's Disease is a genetic disorder caused by a mutation in the HTT gene, which leads to an abnormal repetition of the CAG nucleotide sequence. This mutation results in the production of a faulty protein that damages nerve cells in the brain. Symptoms include uncontrolled movements, cognitive decline, and emotional disturbances. Huntington's Disease is inherited in an autosomal dominant pattern, meaning only one copy of the mutated gene is needed to develop the disorder.
1. What gene is affected in Huntington's Disease?
2. What type of mutation occurs in this disorder?
3. List two symptoms of Huntington's Disease.
4. How is Huntington's Disease inherited?
5. What part of the body is primarily affected?

Passage 2
Cystic Fibrosis is a genetic disorder caused by mutations in the CFTR gene located on chromosome 7. This gene codes for a protein that regulates the movement of chloride ions across cell membranes. When the CFTR protein is defective, chloride transport is disrupted, leading to thick and sticky mucus in the lungs, pancreas, and other organs. Symptoms include persistent cough, lung infections, and difficulty digesting food. Cystic Fibrosis is inherited in an autosomal recessive pattern, meaning a person must inherit two defective copies of the CFTR gene to develop the disease.

Comprehension Questions:
1. What gene is affected in Cystic Fibrosis?
2. How does the mutation affect the body?
3. What are two symptoms of Cystic Fibrosis?
4. How is Cystic Fibrosis inherited?
5. Why does mucus become thick in this disorder?

Answer 1

Mutations passage
1. What is a mutation?
- A mutation is a change in the DNA sequence.

2. What causes point mutations?
- Point mutations are caused by a change, insertion, or deletion of a single nucleotide. They can arise from errors during DNA replication or from environmental factors (radiation, chemicals).

3. How can a point mutation affect a protein?
- A point mutation can be silent (no change in amino acid), missense (one amino acid is changed), or nonsense (creates a stop codon and shortens the protein), altering the protein’s function accordingly.

4. What makes a frameshift mutation different from a point mutation?
- A frameshift mutation is an insertion or deletion of nucleotides in numbers not divisible by three, which shifts the reading frame of codons. A point mutation changes only a single nucleotide (and does not necessarily shift the reading frame).

5. Explain why frameshift mutations often lead to nonfunctional proteins.
- Shifting the reading frame changes every downstream codon, producing a radically different amino acid sequence and often creating an early stop codon, which usually yields a truncated, nonfunctional protein.

Passage 1 — Huntington’s Disease
1. What gene is affected in Huntington's Disease?
- The HTT gene.

2. What type of mutation occurs in this disorder?
- An abnormal expansion (repetition) of the CAG trinucleotide sequence (a CAG repeat expansion).

3. List two symptoms of Huntington's Disease.
- Uncontrolled movements (chorea) and cognitive decline. (Also emotional disturbances.)

4. How is Huntington's Disease inherited?
- Autosomal dominant.

5. What part of the body is primarily affected?
- The brain (nerve cells in the brain).

Passage 2 — Cystic Fibrosis
1. What gene is affected in Cystic Fibrosis?
- The CFTR gene (on chromosome 7).

2. How does the mutation affect the body?
- It produces a defective CFTR protein that disrupts chloride ion transport across cell membranes, impairing fluid balance in secretions.

3. What are two symptoms of Cystic Fibrosis?
- Persistent cough and frequent lung infections. (Also difficulty digesting food.)

4. How is Cystic Fibrosis inherited?
- Autosomal recessive.

5. Why does mucus become thick in this disorder?
- Impaired chloride (and thus water) transport causes secretions to be dehydrated, making mucus thick and sticky.