Question 1

Which of the following best explains why RNA is generally less stable than DNA under cellular conditions?

Accepted Answer

RNA has a ribose sugar with an OH group at the 2' carbon, increasing its chemical reactivity.

Question 2

A scientist finds that a sample of double-stranded DNA contains 18% adenine. According to Chargaff’s rules, what percentage of the DNA is cytosine?

Accepted Answer

$$32\%$$

Question 3

During which phase of the cell cycle does DNA replication occur, and what is the main purpose of this phase?

Accepted Answer

S phase; to duplicate the genetic material so each daughter cell receives a complete set of chromosomes.

Question 4

Which of the following best describes the difference between homologous chromosomes and sister chromatids?

Accepted Answer

Homologous chromosomes are inherited from different parents and may have different alleles, while sister chromatids are identical copies formed during DNA replication.

Question 5

A cell with 12 chromosomes undergoes mitosis and cytokinesis. How many chromosomes and DNA molecules will each daughter cell have immediately after division?

Accepted Answer

12 chromosomes and 12 DNA molecules

Question 6

Which event during meiosis increases genetic variation by exchanging DNA segments between nonsister chromatids?

Accepted Answer

Crossing over during prophase I

Question 7

A woman who is a carrier for an X-linked recessive disorder (X$$^AX$^a) $$has children with a man who is unaffected (X$$^AY). $$What is the probability that a son will be affected by the disorder?

Accepted Answer

$$0.25$$

Question 8

Which of the following best explains why sexual reproduction can be advantageous in changing environments?

Accepted Answer

It generates genetic diversity, increasing the likelihood that some offspring will survive new conditions or pathogens.

Question 9

A testcross is performed between a pea plant with genotype AaBb and a plant with genotype aabb. What is the expected phenotypic ratio among the offspring, assuming independent assortment and complete dominance?

Accepted Answer

1:1:1:1

Question 10

Which of the following statements about cyclin-dependent kinases (Cdks) and cell cycle regulation is correct?

Accepted Answer

Cyclin binding is necessary for Cdk activation, and additional phosphorylation controls further regulate activity.

Question 11

A pedigree shows a trait that appears in every generation, and affected fathers pass the trait to all daughters but no sons. Which inheritance pattern is most likely?

Accepted Answer

X-linked dominant

Question 12

If a fruit fly species has a diploid number of $$2n = 8$$, how many chromosomes and DNA molecules are present in a normal gamete after meiosis II?

Accepted Answer

4 chromosomes and 4 DNA molecules

Question 13

Which of the following best describes the molecular basis for incomplete dominance?

Accepted Answer

The heterozygote produces an intermediate amount of functional product, resulting in an intermediate phenotype.

Question 14

A cell fails to pass the G$$_1$$ checkpoint due to DNA damage. Which protein is most likely responsible for halting the cell cycle or triggering apoptosis?

Accepted Answer

p53

Question 15

In a dihybrid cross AaBb × AaBb, what is the probability of obtaining an offspring with genotype aabb?

Accepted Answer

$$\dfrac{1}{16}$$

Question 16

Which of the following is a direct result of nondisjunction during meiosis I?

Accepted Answer

Two gametes with n + 1 chromosomes and two with n − 1 chromosomes

Question 17

Which of the following best explains why linked genes do not always show perfect co-inheritance?

Accepted Answer

Crossing over during meiosis can produce recombinant chromosomes with new allele combinations.

Question 18

A woman and her partner are both carriers (Aa) for an autosomal recessive disorder. What is the probability that their unaffected child is also a carrier?

Accepted Answer

$$\dfrac{2}{3}$$

Question 19

Which of the following is NOT a function of the major and minor grooves in the DNA double helix?

Accepted Answer

Facilitating the formation of phosphodiester bonds between nucleotides

Question 20

Which of the following best describes the role of MPF (M-phase promoting factor) in the cell cycle?

Accepted Answer

MPF is a protein complex that triggers the cell’s entry into M phase by phosphorylating target proteins.

BIO 111 Study Notes: Nucleic Acids, Cell Cycle, Meiosis, and Mendelian Genetics (EXAM 2)

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