Question 1

Suppose you have engineered a plasmid vector in order to produce a functional animal protein in E. coli. But the product you collect, while it has the correct amino acid sequence, is in fact nonfunctional. What might you try that would have a greater chance of success?

Accepted Answer

D

Question 2

Which of the following is a possible advantage for the environment of having farmers use plants that genetically produce Bt toxin?

Accepted Answer

Plants with genes for Bt toxin are resistant to certain insect pests, which means that farmers who use these plants need to apply less insecticide overall. This reduces chemical pollution and the harmful effects of insecticides on non-target organisms.

Question 3

Current sequencing technologies have major advantages over the dideoxy method because they produce more sequence in less time and at less cost. Which of the following would provide further advantage?

Accepted Answer

Sequencing without the need to amplify the DNA would provide a significant advantage as it would simplify the process, reduce potential errors introduced during amplification, and allow for direct sequencing of small or degraded samples.

Question 4

Snuppy, a male Afghan hound, was created by transferring the nucleus from an ear cell of the male Afghan, Tai, into an enucleated egg from a donor. The embryo was transplanted into a surrogate mother to develop to term. Which of the following animals would be a genetic match for Snuppy if nuclear DNA were tested?

Accepted Answer

Since the nucleus was taken from Tai, the resulting individual (Snuppy) would have the same nuclear DNA as Tai. Therefore, Tai would be a genetic match for Snuppy. The egg donor and surrogate would not contribute nuclear DNA to Snuppy, so they would not be genetic matches.

Question 5

Which of the following vectors would be most efficient to use to amplify fragments ~300 kb in length?

Accepted Answer

YACs (yeast artificial chromosomes) are the most efficient vectors to use for amplifying large fragments, such as ones that are ~300 kb in length. YACs are capable of holding inserts up to 1 Mb, making them ideal for larger genomic regions. BACs (bacterial artificial chromosomes), plasmids, and cosmids are all limited in their insert size, with BACs being the largest at ~200 kb. F1F1F1S1F1F1F10 phage is not used for cloning large fragments.

Question 6

In producing a recombinant plasmid to be used to clone a given donor insert, it is possible to cut both the donor and plasmid with the same restriction enzyme, resulting in complementary sticky ends. Assuming plenty of plasmid DNA is available, why is further selection necessary before the introduction of the plasmid into a cellular system?

Accepted Answer

Even if the donor insert and plasmid are cut with the same restriction enzyme and have complementary sticky ends, there is still a possibility that the donor insert can be inserted into the plasmid in the wrong orientation. This would result in the incorrect expression of the gene of interest or complete inactivation of the gene. Therefore, further selection is necessary to ensure that only recombinant plasmids with the donor insert in the correct orientation are introduced into a cellular system.

Question 7

In 1978, Arber, Smith, and Nathans won the Nobel Prize in Physiology and Medicine for work with restriction enzymes. Which of the following can still be performed without using these enzymes?

Accepted Answer

Genetic mapping does not require the use of restriction enzymes. It involves analyzing the inheritance patterns of genetic markers in order to determine the locations of genes on a chromosome.

Question 8

If genes are introduced into a yeast plasmid to serve as a shuttle vector, the plasmid has the ability to __________.

Accepted Answer

A shuttle vector is a plasmid that can replicate in two or more different host species, such as both yeast and bacteria, and can thus "shuttle" genetic material between these different organisms.

Question 9

In using Agrobacterium tumefaciens to transfer genes into plants, what is transferred from bacterium to plant?

Accepted Answer

In using Agrobacterium tumefaciens to transfer genes into plants, the T-DNA (transfer DNA) is transferred from the bacterium to the plant. The T-DNA is part of the Ti (tumor-inducing) plasmid in the bacterium and is responsible for causing the formation of a tumor or gall on the infected plant. However, researchers have modified the Ti plasmid to remove the tumor-causing genes and replace them with desired genes for plant transformation.

Question 10

Some restriction enzymes cut at specific and unambiguous sequences (e.g., NotI at GCGGCCGC). As such, the distance between two such sites in a large random DNA sequence is 4⁸, assuming a 50% G+C DNA content. However, the sequence recognized by XhoII is said to be ambiguous (Pu-GATC-Py, where Pu = any purine and Py any pyrimidine). What, therefore, is the expected distance between two XhoII sites in a large random sequence?

Accepted Answer

The XhoII recognition sequence is ambiguous, meaning that any purine (A or G) can be present in the first position, and any pyrimidine (C or T) can be present in the fourth position. Thus, there are 4 possible nucleotides for the first position, 4 for the second, 4 for the third (since it has to be A or T), and 4 for the fourth. Therefore, the expected distance between two XhoII sites in a large random DNA sequence is 2 × 4 × 4 × 4 × 4 × 2, which simplifies to 512 base pairs (bp).

Question 11

In selecting recombinant bacteria, cells are chosen that are resistant to a specific antibiotic. How are the bacteria made resistant?

Accepted Answer

The antibiotic resistance gene is encoded in the vector, which is used to introduce the donor insert into the recipient bacterium. The vector typically contains a selectable marker, such as an antibiotic resistance gene, that allows for the identification and selection of successfully transformed cells. Therefore, the bacteria are made resistant to the specific antibiotic by acquiring the antibiotic resistance gene from the vector during the transformation process.

Question 12

In the construction of a YAC library, each chromosome has the advantage of being able to hold very long DNA sequences. However, besides selectable marker(s)the YAC vector must minimally include which of the following?

Accepted Answer

In addition to selectable marker(s), the YAC vector must minimally include centromere, telomeres, and yeast origin. The centromere is necessary for proper segregation during cell division, telomeres protect the ends of the DNA from degradation, and the yeast origin is required for replication within the yeast cell. The bacterial origin (ori) and cos site(s) are not necessary for YAC construction, as YAC cloning relies solely on the properties of yeast cells.

Question 13

In nature, what is the order of events in processing the product of the gene for insulin?

Accepted Answer

The order of events in processing the product of the gene for insulin involves cleavage of 24 amino acids from the N terminus to form proinsulin which is subsequently cleaved to make A and B chains. This is the correct sequence of events for insulin processing in nature.

Question 14

One use of PCR has been to monitor the trafficking of endangered organisms. Suppose that one suspect was accused of illegally importing a specific animal, but the suspect asserts that the young animal had been bred in this country from two resident zoo animals. How would you best proceed?

Accepted Answer

DNA from hair follicles of the supposed zoo parents and of the supposed offspring can be used to compare sequences amplified with primers for a highly polymorphic region. This can establish the relationship between the parents and the offspring, and determine if the offspring was indeed bred in the country or illegally imported. This method is more specific and reliable than using blood cells and looking for sequences found only in illegally traded animals, or using a probe for infectious agents found more frequently in its native country. Treatment with restriction enzymes and using a probe for disease genes common in its native country may not necessarily establish the origin of the animal as it does not take into account the breeding history. Amplifying highly polymorphic regions from zoo and native populations may not be useful as it does not directly compare the suspected animal to its supposed parents.

Question 15

When a transgene is used in mice to knock out a specific function, two problems that might occur are the unintended introduction of multiple copies or abnormal gene expression. The second of these problems is related to __________.

Accepted Answer

Position effect refers to the way that the location of a gene within the chromosome can affect its expression. When a transgene is randomly inserted into the genome, its expression can be influenced by nearby regulatory sequences, leading to abnormal or unintended expression patterns. This is a common issue when using transgenic mice to knock out specific gene functions.

Question 16

You have a DNA sequence of 1600 bp. To characterize it, you decide to make a restriction map. Cutting with the first enzyme, you show by electrophoresis that the fragments produced are 400 and 1200 bp, respectively. After using the second enzyme, you recover 700-bp and 900-bp fragments. After treatment with both enzymes, fragments were 300, 400, and 900 bp. Which is the correct map?

Accepted Answer

The answer of You have a DNA sequence of 1600...

Question 17

Snuppy, a male Afghan hound, was created by transferring the nucleus from an ear cell of the male Afghan, Tai, into an enucleated egg from a donor. The embryo was transplanted into a surrogate mother to develop to term. Which of the following animals would be a genetic match for Snuppy if nuclear DNA were tested and if Snuppy were not a clone, but the product of in vitro fertilization?

Accepted Answer

Snuppy's nuclear DNA would be a match for both Tai (the donor of the nucleus) and the egg donor (the donor of the cytoplasm).

Question 18

Snuppy, a male Afghan hound, was created by transferring the nucleus from an ear cell of the male Afghan, Tai, into an enucleated egg from a donor. The embryo was transplanted into a surrogate mother to develop to term. Which of the following animals would be a genetic match for Snuppy if mitochondrial DNA were tested?

Accepted Answer

Mitochondrial DNA is inherited maternally, so Snuppy would have inherited his mitochondrial DNA from the egg donor.

Question 19

Whether libraries are cDNA or genomic, whether amplification is based on PCR or cloning, and whether screening is done with northern or Southern blotting or probes, are all decisions based on which of the following?

Accepted Answer

Complementarity is the basis for all of the decisions listed in the question.

Question 20

In forensics, the laws in the United States and elsewhere allow the establishment of databases of PCR amplification of short tandem repeats (STRs)of the Y chromosome. Which of these statements would provide an appropriate basis for making such databases divided by ethnicity?

Accepted Answer

Different heritage groups have different levels of Y chromosome polymorphisms, which means that creating databases divided by ethnicity would allow for more accurate identification of suspects and increase the chances of solving cases. Additionally, this approach is based on scientific evidence and is not discriminatory, as it is solely focused on DNA analysis.

Quiz 17: Applications of Recombinant Dna Technology and Reverse Genetics