Q: During PCR, if you start with a single double-stranded DNA molecule, how many double-stranded DNA molecules will you have after 7 cycles? Use the formula $$N = N_0$ \times 2^n.$$

$$N = 1 \times 2^7$ = 128$$ molecules

Question 1

A researcher is using the restriction enzyme EcoRI, which recognizes the sequence 5'-GAATTC-3'. If a bacterial genome is 4 million base pairs long and has a random distribution of nucleotides, approximately how many EcoRI sites would you expect in the genome? (Assume equal base composition.)

Accepted Answer

About 1,000 sites, since EcoRI recognizes a 6-base sequence and $$4^6 = 4096$; 4$$,000,000 / 4096 \approx 977$$.

Question 2

Which of the following best describes the role of DNA ligase in recombinant DNA technology?

Accepted Answer

It joins together DNA fragments by catalyzing the formation of phosphodiester bonds between adjacent nucleotides.

Question 3

A scientist digests a circular plasmid with a single restriction enzyme and observes two DNA fragments after gel electrophoresis. Which of the following best explains this result?

Accepted Answer

The plasmid contains two recognition sites for the restriction enzyme, resulting in two fragments.

Question 4

During PCR, if you start with a single double-stranded DNA molecule, how many double-stranded DNA molecules will you have after 7 cycles? Use the formula $$N = N_0$ 	imes 2^n.$$

Accepted Answer

$$N = 1 	imes 2^7$ = 128$$ molecules

Question 5

Which of the following statements about the Sanger method of DNA sequencing is correct?

Accepted Answer

It uses dideoxynucleotides to terminate DNA synthesis at specific bases, generating fragments of varying lengths.

Question 6

A researcher wants to determine whether a gene has been successfully inserted into a plasmid in the correct orientation. Which experimental approach would be most effective?

Accepted Answer

Digest the plasmid with restriction enzymes that flank the insertion site and analyze the fragment sizes by gel electrophoresis.

Question 7

Which of the following best describes a molecular probe used in recombinant DNA technology?

Accepted Answer

A labeled single-stranded DNA or RNA sequence that is complementary to the target sequence and can hybridize to it.

Question 8

Which of the following is a key difference between knock-in and knock-out transgenic organisms?

Accepted Answer

Knock-in organisms have a specific gene inserted or replaced, while knock-out organisms have a gene inactivated or deleted.

Question 9

Which of the following statements about CRISPR-Cas9 genome editing is correct?

Accepted Answer

It uses a guide RNA to direct the Cas9 nuclease to a specific DNA sequence, where it introduces a double-strand break.

Question 10

Before the advent of whole-genome sequencing, which of the following was a major limitation in identifying genes?

Accepted Answer

Gene identification relied on known phenotypes or protein products, making it difficult to find genes with unknown functions.

Question 11

Which of the following is a disadvantage of whole-genome sequencing?

Accepted Answer

It generates large amounts of data that require complex computational analysis and storage.

Question 12

Which of the following best describes the difference between orthologs and paralogs?

Accepted Answer

Orthologs are genes in different species that evolved from a common ancestral gene, while paralogs are genes within the same species that arose by duplication.

Question 13

Which of the following is a hallmark feature used in computational annotation to identify genes in an unknown DNA sequence?

Accepted Answer

The presence of open reading frames (ORFs) with start and stop codons.

Question 14

Which of the following best describes the difference between DNA microarray and RNA sequencing (RNA-seq) in transcriptome analysis?

Accepted Answer

RNA-seq can detect novel transcripts and alternative splicing events, while microarrays are limited to known sequences.

Question 15

A patient is suspected of having a genetic disorder caused by a single nucleotide change. Which technique would be most appropriate for confirming the diagnosis?

Accepted Answer

Restriction fragment length polymorphism (RFLP) analysis, if the mutation creates or abolishes a restriction site.

Question 16

Which of the following is a limitation of using RFLP analysis in genetic testing?

Accepted Answer

It can only detect mutations that alter restriction enzyme recognition sites.

Question 17

Which of the following is a major finding of the Human Genome Project regarding the organization of the human genome?

Accepted Answer

The human genome contains a large amount of non-coding DNA, including repetitive sequences and transposable elements.

Question 18

Which of the following best describes the use of transgenic crops in agriculture?

Accepted Answer

They can be engineered to express traits such as pest resistance or improved nutritional content, addressing commercial and societal needs.

Question 19

A couple, both carriers of a recessive genetic disorder, want to know the probability that their child will be affected. What is the probability, and which equation should be used?

Accepted Answer

The probability is $$\frac{1}{4}$$, using a Punnett square for two heterozygous parents ($$Aa 	imes Aa).$$

Question 20

Which of the following best describes the field of proteomics?

Accepted Answer

It is the large-scale study of all proteins expressed by a genome, including their structure, function, and interactions.

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