Question 1

A mutation in a gene encoding an enzyme in a metabolic pathway prevents the conversion of compound B to compound C. If a mutant strain can grow only when provided with compound C or later intermediates, but not with compound A or B, what does this indicate about the pathway?

Accepted Answer

The pathway is linear and the mutation blocks the step converting B to C.

Question 2

Which of the following best describes the difference between a loss-of-function and a gain-of-function mutation?

Accepted Answer

Loss-of-function mutations reduce or eliminate protein activity, while gain-of-function mutations create a new or enhanced activity.

Question 3

A DNA sequence changes from 5'-ATG GAA TGC-3' to 5'-ATG GAG TGC-3'. What type of mutation has occurred, and what is the likely effect at the protein level?

Accepted Answer

A transition resulting in a missense mutation.

Question 4

Which DNA repair mechanism is primarily responsible for removing thymine dimers caused by UV light?

Accepted Answer

Nucleotide excision repair

Question 5

A maize kernel shows a variegated phenotype due to the presence of Ds and Ac transposable elements. What is the molecular explanation for this phenotype?

Accepted Answer

Ac provides transposase for Ds to move, causing somatic excision and mosaicism.

Question 6

Which of the following chromosomal aberrations is most likely to result in a dicentric chromosome during meiosis?

Accepted Answer

Paracentric inversion

Question 7

In the lac operon, what is the effect of a mutation that inactivates the lacI gene (repressor) in the presence and absence of lactose?

Accepted Answer

The operon is always on, regardless of lactose presence.

Question 8

Which of the following best explains why attenuation of the trp operon is restricted to prokaryotes?

Accepted Answer

Prokaryotes lack a nucleus, allowing transcription and translation to occur simultaneously.

Question 9

Which epigenetic modification is most commonly associated with gene silencing in eukaryotes?

Accepted Answer

DNA methylation

Question 10

A patient is diagnosed with Down syndrome (trisomy 21). Which meiotic event most likely led to this condition?

Accepted Answer

Nondisjunction during meiosis I in the mother

Question 11

Which of the following statements about allopolyploids is correct?

Accepted Answer

Allopolyploids result from hybridization between two different species followed by chromosome doubling.

Question 12

Which of the following best describes the role of somatic recombination in antibody diversity?

Accepted Answer

It rearranges V, D, and J gene segments in B cells to generate diverse antibodies.

Question 13

In Drosophila, which maternal-effect gene establishes the anterior region of the embryo?

Accepted Answer

Bicoid

Question 14

A flower mutant in Arabidopsis lacks petals and stamens but has normal sepals and carpels. Which class of floral organ identity genes is most likely mutated?

Accepted Answer

Class B genes

Question 15

Which of the following regulatory DNA sequences acts as a boundary to prevent the spread of heterochromatin and block enhancer-promoter interactions?

Accepted Answer

Insulator

Question 16

A point mutation changes a codon from UAU (tyrosine) to UAA (stop). What type of mutation is this?

Accepted Answer

Nonsense mutation

Question 17

Which of the following best explains why most cells in a multicellular organism have different functions despite having the same DNA?

Accepted Answer

Gene expression is regulated differently in each cell type.

Question 18

Which process is responsible for correcting errors made by DNA polymerase during replication?

Accepted Answer

3'-5' exonuclease proofreading activity

Question 19

A gene is expressed only when a specific transcription factor is present. Which of the following best describes the role of the transcription factor?

Accepted Answer

It binds to regulatory DNA sequences to activate transcription.

Genetics Study Guide: Biochemical Pathways, Mutations, Regulation, and Development

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