Q: A scientist uses PCR to amplify a DNA segment. If she starts with 10 copies of DNA and runs 5 cycles, how many copies will she have at the end, assuming perfect doubling each cycle?

$$10 \times 2^5$ = 320$$ copies

Question 1

A scientist is studying a cell that has 24 chromosomes during G1 phase. After this cell completes S phase and then undergoes mitosis, how many chromosomes and chromatids will each daughter cell have immediately after cytokinesis?

Accepted Answer

24 chromosomes and 24 chromatids

Question 2

Which of the following best explains why DNA wraps around histones in the nucleus?

Accepted Answer

DNA is negatively charged and histones are positively charged, so they attract each other.

Question 3

A cell fails to pass the G2 checkpoint. Which of the following is the most likely reason?

Accepted Answer

The DNA was not fully or correctly replicated.

Question 4

During meiosis, crossing over occurs at which stage, and what is its genetic significance?

Accepted Answer

Prophase I; it increases genetic diversity by exchanging DNA between homologous chromosomes.

Question 5

A woman who is heterozygous for a recessive X-linked disorder (XᴬXᵃ) has children with a man who does not have the disorder (XᴬY). What is the probability that their son will have the disorder?

Accepted Answer

$$0.5$$

Question 6

A plant with genotype AaBb is crossed with another plant of the same genotype. What is the expected phenotypic ratio among the offspring, assuming independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 7

A DNA strand has the sequence 5'-ATG CCA TGA-3'. What is the corresponding mRNA sequence produced during transcription?

Accepted Answer

5'-AUG CCA UGA-3'

Question 8

Which enzyme is responsible for joining Okazaki fragments on the lagging strand during DNA replication?

Accepted Answer

DNA ligase

Question 9

A patient with xeroderma pigmentosum is highly sensitive to sunlight and develops skin cancers easily. Which DNA repair mechanism is defective in this condition?

Accepted Answer

Nucleotide excision repair

Question 10

Which of the following best describes the function of the MPF (Mitosis Promoting Factor) complex in the cell cycle?

Accepted Answer

It triggers the cell's entry into mitosis when cyclin binds to CDK.

Question 11

A child is born with Down syndrome (trisomy 21). Which meiotic error most likely caused this condition?

Accepted Answer

Nondisjunction during meiosis I or II, resulting in a gamete with $$n+1$$ chromosomes.

Question 12

Which of the following statements about the genetic code is correct?

Accepted Answer

It is nearly universal, allowing genes from one species to be expressed in another.

Question 13

A scientist uses PCR to amplify a DNA segment. If she starts with 10 copies of DNA and runs 5 cycles, how many copies will she have at the end, assuming perfect doubling each cycle?

Accepted Answer

$$10 	imes 2^5$ = 320$$ copies

Question 14

Which of the following best explains why males are more likely than females to express recessive X-linked traits?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will be expressed.

Question 15

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

Accepted Answer

Nonsense mutation

Question 16

Which of the following is a real-world application of recombinant DNA technology?

Accepted Answer

Producing human insulin in bacteria for diabetes treatment

Question 17

A scientist wants to insert a human gene into a bacterial plasmid. Which enzyme should she use to cut both the gene and the plasmid at specific sequences?

Accepted Answer

Restriction enzyme

Question 18

Which of the following best describes the difference between leading and lagging strand synthesis during DNA replication?

Accepted Answer

The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized in short fragments away from the fork.

Question 19

Which of the following best explains why telomeres shorten with each cell division in most somatic cells?

Accepted Answer

DNA polymerase cannot fully replicate the ends of linear chromosomes, so a small portion is lost each time.

Question 20

A researcher uses CRISPR-Cas9 to correct a mutation in a patient's gene. What is the role of the guide RNA in this process?

Accepted Answer

It directs the Cas9 enzyme to the specific DNA sequence to be cut.

General Biology Study Guide: Cell Cycle, Genetics, DNA Replication, Gene Expression, and Biotechnology

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