genetics test 2 ch 16 HW

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doncheto
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288806
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genetics test 2 ch 16 HW
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2014-11-10 15:00:04
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  1. A gene mutation changes an AT base pair to a GC pair. This causes a gene to encode a truncated protein that is nonfunctional. An organism that carries this mutation cannot survive at high temperatures. Make a list of all the genetic terms that could be used to
    describe this type of mutation.
    • It is a gene mutation, a point mutation, a base substitution, a transition mutation, a
    • deleterious mutation, a mutant allele, a nonsense mutation, a conditional mutation, and a temperature-sensitive lethal mutation.
  2. How would each of the following types of mutations affect the amount of functional protein that is expressed from a gene?
    A. Nonsense
    B. Missense
    C. Up promoter mutation
    D. Mutation that affects splicing
    Nonsense - If the mutation is closer to the beginning the sequence it will mostly likely inhibit protein function.

    • Missence - Depending if the amino acid is critical to the
    • formation of the protein.

    Up promoter mutation - There would be an increase in functional protein.

    Mutation that affects splicing - It may affect protein function if the alteration in splicing changes an exon in the mRNA  that results in a protein with a perturbed structure.
  3. Question Are each of the
    following mutations silent, missense, nonsense, or frameshift mutations? The
    original DNA strand is 5ʹ ATGGGACTAGATACC–3ʹ. (Note: Only the coding strand is shown; the first codon is methionine.)
    A. 5ʹ–ATGGGTCTAGATACC–3ʹ
    B. 5ʹ–ATGCGACTAGATACC–3ʹ
    C. 5ʹ–ATGGGACTAGTTACC–3ʹ
    D. 5ʹ–ATGGGACTAAGATACC–3ʹ
    • A. 5ʹ–ATGGGTCTAGATACC–3ʹ --- silent
    • because it still codes for the same amino acid

    • B. 5ʹ–ATGCGACTAGATACC–3ʹ ---missense
    • because a different amino acid is encoded by CGA compared to GGA.

    • C. 5ʹ–ATGGGACTAGTTACC–3ʹ --- because a
    • different amino acid is encoded by GTT compared to GAT

    • D. 5ʹ–ATGGGACTAAGATACC–3ʹ --- frame
    • shift because a base pair was inserted
  4. Explain how a mutagen can interfere with DNA replication to cause a mutation. Give two
    examples.
    • A mutagen can create thymine dimers which prevent DNA polymerase from sliding
    • through and adding to the new strand.
  5. Achondroplasia is a rare form of dwarfism. It is caused by an autosomal dominant mutation within a single gene. Among 1,422,000 live births, the number of babies born with achondroplasia was 31. Among those 31 babies, 18 of them had one parent with achondroplasia.
    The remaining babies had two unaffected parents. What is the mutation frequency for this disorder among these 1,422,000 babies? What is the mutation rate for achondroplasia?
    The mutation frequency is the total number of mutant alleles divided by the total number of alleles in the population. If there are 1,422,000 babies, there are 2,844,000 copies of this gene (because each baby has 2 copies). The mutation frequency is31/2,844,000, which equals 1.09 × 10-5. The mutation rate is the number of new mutations per generation. There are 13 babies who did not have a parent with achondroplasia; thus,thirteen is the number of new mutations. If we calculate the mutation rate as the number of new mutations in a given gene per generation, then we should divide 13 by 2,844,000. In this case, the mutation rate would be 4.6 × 10-6.
  6. What is the underlying genetic defect that causes xeroderma pigmentosum?
    How can the symptoms of this disease be explained by the genetic defect?
    The underlying genetic defect that causes xeroderma pigmentosum is a defect in one of the genes that encode a polypeptide involved with nucleotide excision repair. These individuals are defective in repairing DNA abnormalities such as thymine dimers and abnormal bases. Therefore, they are very sensitive to environmental agents such as UV light. Because they are defective at repair, UV light is more likely to cause mutations in these people compared to unaffected individuals. For this reason, people with XP develop pigmentation abnormalities and premalignant lesions, and have a high predisposition to skin cancer.

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