Question 1

A common mutation in cystic fibrosis is a three-base-pair deletion at position 508 of the CFTR protein. What is the most likely consequence of this mutation?

Accepted Answer

The deletion of a single amino acid in the protein

Question 2

During DNA replication, DNA polymerase proofreads and corrects errors. If proofreading fails, which repair mechanism is activated to fix mismatches?

Accepted Answer

Mismatch repair

Question 3

Which enzyme is responsible for recognizing and excising a damaged base during base excision repair?

Accepted Answer

DNA glycosylase

Question 4

In nucleotide excision repair (NER), what is the typical number of nucleotides excised in E. coli during the repair of a UV-induced thymine dimer?

Accepted Answer

13 nucleotides

Question 5

A double-strand break in DNA is extremely dangerous. Which repair pathway is activated in G1 phase prior to replication to fix such breaks?

Accepted Answer

Nonhomologous end joining

Question 6

Which of the following best describes the mechanism of homologous recombination repair for double-strand breaks?

Accepted Answer

The 5' end is digested, leaving a 3' overhang that aligns with a complementary sequence on the sister chromatid

Question 7

Transposable elements (TEs) are also known as 'jumping genes.' Which feature is characteristic of DNA transposons?

Accepted Answer

They contain inverted terminal repeats (ITRs) recognized by transposase

Question 8

Barbara McClintock discovered the Ac-Ds system in maize. What happens when Ds transposes into the W gene in the presence of Ac?

Accepted Answer

W gene expression is inhibited, producing a mutant effect

Question 9

Retrotransposons move within the genome using an RNA intermediate. Which enzymes are encoded by LTR retrotransposons?

Accepted Answer

Integrase and reverse transcriptase

Question 10

The white-apricot mutation in Drosophila is caused by the insertion of a copia element into the second intron of the white gene. What is the result of this mutation?

Accepted Answer

Prematurely terminated mRNA containing only two exons is produced

Question 11

Which of the following is a potential effect of transposons in the genome?

Accepted Answer

All of the above

Question 12

A child with hemophilia was found to have a LINE element inserted at two points within a gene. What does this illustrate about transposable elements in humans?

Accepted Answer

Transposable elements can cause genetic diseases by disrupting gene function

Question 13

Which repair mechanism is most likely to fix a thymine dimer caused by UV radiation in human cells?

Accepted Answer

Nucleotide excision repair

Question 14

If a transposon inserts into the regulatory region of a gene, what is a likely outcome?

Accepted Answer

The gene's transcription may be altered

Question 15

Which of the following equations best represents the probability of a mutation occurring per base pair per replication, given a mutation rate $$\mu$$ and a genome size $$N$$?

Accepted Answer

$$P = \mu 	imes N$$

Question 16

Which step is NOT part of the base excision repair pathway?

Accepted Answer

uvr gene products excise a bulky lesion

Question 17

Which of the following statements about nonhomologous end joining (NHEJ) is correct?

Accepted Answer

NHEJ is activated in G1 phase and directly ligates broken DNA ends

Question 18

Which of the following is a plausible consequence of identical transposable elements being present at multiple locations in the genome?

Accepted Answer

Increased likelihood of transposon recombination

Question 19

Which repair mechanism is most likely to be activated after DNA replication has skipped over a lesion such as a thymine dimer?

Accepted Answer

Postreplication repair

Question 20

Which of the following best describes the 'copy and paste' mechanism of retrotransposons?

Accepted Answer

Retrotransposons are transcribed into RNA, then reverse transcribed into DNA and inserted elsewhere

Ch 14 P2 Gene Mutation, DNA Repair, and Transposition (Essentials of Genetics, Ch. 14) – Study Notes

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