Question 1

Which of the following best describes a paracentric inversion, and what is a likely consequence during meiosis in a heterozygote?

Accepted Answer

A paracentric inversion does not include the centromere and does not change the lengths of chromosome arms; it can result in dicentric bridges and acentric fragments during meiosis.

Question 2

A reciprocal translocation between two nonhomologous chromosomes can lead to which of the following segregation patterns during meiosis, and what is the genetic consequence?

Accepted Answer

Alternate segregation, resulting in gametes with a complete and balanced set of genetic information.

Question 3

Which chromosomal abnormality is most commonly associated with familial Down syndrome, and what is the chromosomal mechanism?

Accepted Answer

A Robertsonian translocation involving chromosomes 14 and 21, resulting in a large metacentric chromosome and loss of small fragments.

Question 4

Which of the following best describes a missense mutation?

Accepted Answer

A mutation that results in a new triplet code for a different amino acid.

Question 5

What is the molecular consequence of a frameshift mutation?

Accepted Answer

It alters the reading frame of the gene, potentially changing every amino acid downstream of the mutation.

Question 6

Which of the following is a likely result of replication slippage in a region of repetitive DNA?

Accepted Answer

An increase or decrease in the number of repeat units, leading to insertion or deletion mutations.

Question 7

Which DNA repair mechanism is responsible for correcting mismatches that escape proofreading during replication, and how does it distinguish the newly synthesized strand?

Accepted Answer

Mismatch repair, which recognizes the unmethylated strand as the newly synthesized one.

Question 8

Which of the following mutagens acts by inserting itself between DNA base pairs, causing distortions and potential frameshift mutations?

Accepted Answer

Intercalating agents such as ethidium bromide.

Question 9

A patient with xeroderma pigmentosum is highly sensitive to sunlight and develops skin cancers at a young age. Which DNA repair pathway is defective in this disorder?

Accepted Answer

Nucleotide excision repair (NER)

Question 10

Which of the following statements about transposable elements in humans is correct?

Accepted Answer

LINEs and SINEs are types of transposable elements that make up a significant portion of the human genome.

Question 11

Which of the following best explains why mutations occur more frequently in males than females in humans?

Accepted Answer

Male germ cells undergo more rounds of DNA replication, increasing the chance for replication errors.

Question 12

Which of the following is a consequence of a tautomeric shift in a DNA base during replication?

Accepted Answer

It can result in non-complementary base pairing, leading to a point mutation.

Question 13

Which of the following best describes the effect of UV light on DNA?

Accepted Answer

It induces the formation of pyrimidine dimers, which distort the DNA helix and can block replication.

Question 14

What is the primary difference between homologous recombination repair and nonhomologous end joining in double-strand break repair?

Accepted Answer

Homologous recombination repair uses a sister chromatid as a template for accurate repair, while nonhomologous end joining directly ligates the broken ends without a template.

Question 15

Which of the following is a real-life example of a disease caused by expansion of a triplet repeat, and what is the underlying molecular mechanism?

Accepted Answer

Fragile X syndrome, caused by replication slippage leading to increased CGG repeats in the FMR-1 gene.

Question 16

Which of the following best describes the function of DNA glycosylase in base excision repair?

Accepted Answer

It recognizes and removes damaged bases, creating an abasic site.

Question 17

Which of the following is a plausible outcome if a transposable element inserts into the promoter region of a gene?

Accepted Answer

The gene may be silenced or aberrantly expressed, depending on the orientation and sequence of the transposable element.

Question 18

Which of the following best explains why alternate segregation in a translocation heterozygote produces viable gametes, while adjacent segregation does not?

Accepted Answer

Alternate segregation separates balanced chromosomes, while adjacent segregation leads to duplications and deficiencies.

Chromosomal Variations, Mutations, and DNA Repair Mechanisms

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