During gel electrophoresis, why do DNA fragments move toward the positive electrode?
They carry negative charges on their phosphate groups
✓
They carry positive charges on their nitrogenous bases
They are pulled along by the staining dye
They are less dense than the gel
Correct Answer
They carry negative charges on their phosphate groups
The phosphate groups in the DNA backbone are negatively charged at neutral or alkaline pH, so an electric field draws the fragments toward the positive electrode. Saying they carry positive charges on their nitrogenous bases is wrong because the net charge of DNA is negative. Saying they are pulled along by the staining dye is wrong because the dye only makes DNA visible. Saying they are less dense than the gel is wrong because density is not what drives the movement.
Category: Lab Techniques
Question 2
After a gel electrophoresis run, which DNA fragments are found farthest from the wells where the samples were loaded?
The largest fragments
The smallest fragments
✓
The fragments richest in guanine
The fragments loaded first
Correct Answer
The smallest fragments
Small fragments slip through the pores of the gel more easily than large ones, so they travel the greatest distance. The largest fragments move slowest and stay nearest the wells. The fragments richest in guanine do not move differently, because separation depends on size. The fragments loaded first have no advantage, because all samples start moving when the current is switched on.
Category: Lab Techniques
Question 3
In the polymerase chain reaction, what happens when the reaction mixture is heated to about 95 °C?
Primers bind to the template
New strands are built from nucleotides
The two DNA strands separate
✓
The DNA is cut into fragments
Correct Answer
The two DNA strands separate
Heating to about 95 °C breaks the hydrogen bonds between base pairs, denaturing the double helix into single strands. Primers bind to the template during the cooler annealing step, around 50 °C. New strands are built from nucleotides during extension, at about 72 °C. The DNA is cut into fragments by restriction enzymes, which are not part of PCR.
Category: Lab Techniques
Question 4
What does the polymerase chain reaction accomplish?
It cuts DNA at specific sequences
It separates DNA fragments by size
It inserts genes into bacterial cells
It makes many copies of a specific DNA region
✓
Correct Answer
It makes many copies of a specific DNA region
PCR repeats cycles of heating and cooling so that the targeted region doubles in number each cycle, turning a few copies into millions. Cutting DNA at specific sequences is done by restriction enzymes. Separating DNA fragments by size is done by gel electrophoresis. Inserting genes into bacterial cells is part of molecular cloning, not PCR.
Category: Lab Techniques
Question 5
Which enzymes, produced by bacteria as a defense against foreign DNA, recognize specific short DNA sequences and cut the DNA at those sites?
Restriction enzymes
✓
DNA polymerases
Helicases
Proteases
Correct Answer
Restriction enzymes
Restriction enzymes, also called restriction endonucleases, cut DNA at defined recognition sequences, which makes them the cutting tool of molecular cloning. DNA polymerases build DNA rather than cut it. Helicases unwind DNA without cutting it. Proteases break down proteins, not DNA.
Category: Molecular Cloning
Question 6
What are the short, single-stranded overhangs left when an enzyme makes a staggered cut across double-stranded DNA?
Blunt ends
Sticky ends
✓
Primers
Telomeres
Correct Answer
Sticky ends
Sticky ends are overhangs of a few unpaired nucleotides; ends made by the same enzyme are complementary and can base pair with each other. Blunt ends are made by a straight cut and have no overhang. Primers are short sequences that start DNA synthesis. Telomeres are the repeated sequences at the ends of eukaryotic chromosomes.
Category: Molecular Cloning
Question 7
Bacteria are mixed with plasmids that carry an ampicillin resistance gene and then grown on medium containing ampicillin. What does growing them on ampicillin accomplish?
It kills bacteria that took up a recombinant plasmid
It makes the bacteria divide more quickly
It kills bacteria that did not take up a plasmid
✓
It cuts the plasmids open for new DNA
Correct Answer
It kills bacteria that did not take up a plasmid
Only bacteria carrying the plasmid, with its resistance gene, can survive the antibiotic, so the step selects for cells that took up a plasmid. Saying it kills bacteria that took up a recombinant plasmid is wrong because those cells carry the resistance gene too. Saying it makes the bacteria divide more quickly is wrong because ampicillin kills sensitive cells rather than speeding growth. Saying it cuts the plasmids open is wrong because cutting is done by restriction enzymes.
Category: Molecular Cloning
Question 8
A plasmid that has had a human gene spliced into it is an example of what?
Genomic DNA
Mitochondrial DNA
Ribosomal DNA
Recombinant DNA
✓
Correct Answer
Recombinant DNA
Recombinant DNA is DNA that combines sequences from different sources, such as a bacterial plasmid carrying a human gene. Genomic DNA is an organism's own complete set of DNA. Mitochondrial DNA is the small genome inside mitochondria. Ribosomal DNA is the set of genes that code for rRNA.
Category: Molecular Cloning
Question 9
Dolly the sheep was made by fusing a mammary cell from one sheep with an egg cell whose nucleus had been removed, and the embryo was carried by a third sheep. Dolly was a genetic clone of which animal?
The sheep that donated the mammary cell
✓
The sheep that donated the egg cell
The surrogate ewe that carried her
A mix of the egg donor and the surrogate
Correct Answer
The sheep that donated the mammary cell
The donor nucleus holds the genetic instructions, so Dolly matched the sheep that supplied the mammary cell. The sheep that donated the egg cell provided cytoplasm but not nuclear DNA, since the egg's nucleus was removed. The surrogate ewe that carried her gave no genetic material. A mix of the egg donor and the surrogate would require their DNA to combine, which does not happen in this procedure.
Category: Cloning and Transgenics
Question 10
What term describes an organism that has received DNA from a different species?
Haploid
Transgenic
✓
Polyploid
Heterozygous
Correct Answer
Transgenic
A transgenic organism carries foreign DNA from another species, such as a plant carrying a bacterial gene. Haploid describes a cell with one set of chromosomes. Polyploid describes a cell with more than two complete sets. Heterozygous describes having two different alleles of a gene.
Category: Cloning and Transgenics
Question 11
A researcher deletes a gene of known sequence from a mouse and watches for changes in its phenotype to learn what the gene does. What is this approach called?
Classical genetics
Selective breeding
Reverse genetics
✓
Linkage analysis
Correct Answer
Reverse genetics
Reverse genetics starts with a known DNA sequence and asks what happens when that gene is mutated, deleted or overexpressed. Classical genetics works in the other direction, from an observed phenotype to the gene behind it. Selective breeding chooses parents with desired traits. Linkage analysis maps genes by how often they are inherited together.
Category: Cloning and Transgenics
Question 12
Why was human insulin made by recombinant bacteria an improvement over insulin taken from pigs?
Pig insulin did not lower blood glucose at all
Pig insulin could be taken only by mouth
Pig insulin worked only in children
Pig insulin caused allergic reactions in some patients
✓
Correct Answer
Pig insulin caused allergic reactions in some patients
Pig insulin caused allergic reactions in some people, while recombinant bacteria can make insulin identical to the human form in large amounts. Saying pig insulin did not lower blood glucose is wrong because it was used to treat diabetes for decades. Saying it could be taken only by mouth is wrong because insulin is broken down in the digestive tract and must be injected. Saying it worked only in children is wrong because it treated patients of all ages.
Category: Medical Biotechnology
Question 13
In gene therapy, how is a working copy of a gene usually delivered into a patient's cells?
Inside a virus used as a vector
✓
By injecting the purified protein
By transplanting a cloned embryo
By exposing the cells to ultraviolet light
Correct Answer
Inside a virus used as a vector
Gene therapy usually packages the normal gene in a modified virus, such as an adenovirus, which infects the target cells and delivers the DNA. Injecting the purified protein replaces the product but does not deliver a gene. Transplanting a cloned embryo is not part of gene therapy. Exposing the cells to ultraviolet light damages DNA rather than adding a gene.
Category: Medical Biotechnology
Question 14
Which bacterium, which naturally causes tumors in plants, is used to transfer chosen genes into plant cells?
Bacillus thuringiensis
Agrobacterium tumefaciens
✓
Escherichia coli
Streptococcus pneumoniae
Correct Answer
Agrobacterium tumefaciens
Agrobacterium tumefaciens transfers part of its own plasmid DNA into the genome of the plants it infects, and researchers modify that plasmid to carry the genes they want to add. Bacillus thuringiensis is the source of the Bt insecticidal toxin gene, not the delivery tool. Escherichia coli is the workhorse for cloning in bacteria, not for transforming plants. Streptococcus pneumoniae is a human pathogen.
Category: Agricultural Biotechnology
Question 15
What trait do crops gain when they are engineered to carry a toxin gene from Bacillus thuringiensis?
Tolerance of drought
Longer shelf life
Resistance to plant-eating insects
✓
Resistance to herbicides
Correct Answer
Resistance to plant-eating insects
The Bt toxin is a protein that becomes active in the gut of many plant-feeding insects, which stop feeding and die, so crops that make it protect themselves. Tolerance of drought comes from other genes. Longer shelf life was the goal of the FlavrSavr tomato. Resistance to herbicides is a different engineered trait.
Category: Agricultural Biotechnology
Question 16
On a physical map of a chromosome, in what units is the distance between genes measured?
Recombination frequency
Numbers of chromosomes
Numbers of amino acids
Numbers of base pairs
✓
Correct Answer
Numbers of base pairs
A physical map shows actual distances along the DNA in nucleotides, giving the fine detail of a chromosome region. Recombination frequency is the measure used on a genetic map. Numbers of chromosomes cannot measure distance within one chromosome. Numbers of amino acids describe proteins, not DNA.
Category: Genomics and Proteomics
Question 17
Which field uses a person's genome sequence to choose the drug likely to be most effective and least toxic for that person?
Pharmacogenomics
✓
Metagenomics
Proteomics
Epigenetics
Correct Answer
Pharmacogenomics
Pharmacogenomics studies how an individual's genetic makeup affects drug response and safety. Metagenomics studies the combined genomes of many species in an environment. Proteomics studies the full set of proteins in a cell. Epigenetics studies changes in gene activity that do not alter the DNA sequence.
Category: Genomics and Proteomics
Question 18
What is a proteome?
The full set of genes in an organism
The full set of proteins made by a cell type
✓
The amino acid sequence of one protein
The set of enzymes that copy DNA
Correct Answer
The full set of proteins made by a cell type
A proteome is the complete set of proteins produced by a given cell type, and it changes with conditions even though the genome does not. The full set of genes in an organism is its genome. The amino acid sequence of one protein is that protein's primary structure. The set of enzymes that copy DNA is the replication machinery.
Category: Genomics and Proteomics
Question 19
Why is mitochondrial DNA often used to trace genealogy?
It is inherited equally from both parents
It never changes from one generation to the next
It is usually inherited only from the mother
✓
It is identical in all members of a species
Correct Answer
It is usually inherited only from the mother
In most multicellular organisms, mitochondria and their DNA come from the egg, so they follow a single maternal line back through the generations. Saying it is inherited equally from both parents is wrong because the father usually contributes no mitochondria. Saying it never changes is wrong because mitochondrial DNA actually mutates rapidly, which makes it useful for studying evolutionary relationships. Saying it is identical in all members of a species is wrong because it differs among maternal lines.
Category: Genomics and Proteomics
Question 20
In CRISPR gene editing, what directs the Cas nuclease to a chosen location in the DNA?
A DNA primer
A repressor protein
A ribosomal subunit
A synthetic guide RNA
✓
Correct Answer
A synthetic guide RNA
The guide RNA is designed to match the target sequence, and it leads the Cas nuclease to that site, where the enzyme cuts the DNA. A DNA primer starts DNA synthesis in replication or PCR. A repressor protein blocks transcription of genes. A ribosomal subunit takes part in translation.
Category: Genomics and Proteomics