Question 1

If integration of DNA provided by pronuclear injection occurs after three cell divisions, the resulting mouse will

Accepted Answer

If integration of the DNA occurs after three cell divisions, not all cells will have the transgene, resulting in a mosaic mouse with some cells containing the transgene and others not.

Question 2

What is the purpose of the P element in the creation of transgenic Drosophila?

Accepted Answer

The P element is used in the creation of transgenic Drosophila primarily because it can efficiently transfer DNA into Drosophila chromosomes, facilitating the integration of foreign DNA into the fly's genome for genetic studies and manipulation.

Question 3

What is a possible disadvantage of using genetically modified crops?

Accepted Answer

The transgene from genetically modified (GM) crops can potentially transfer to wild plants through cross-pollination or other means, which might lead to unintended ecological consequences.

Question 4

The coding sequence of the green fluorescent protein gene (GFP)is placed under the control of an enhancer active in neurons.When this transgene is introduced into flies, GFP will be expressed in

Accepted Answer

The enhancer active in neurons ensures that the GFP gene is expressed specifically in neurons or a subset of neurons, depending on the specificity of the enhancer. This allows for targeted expression rather than ubiquitous expression in all cells.

Question 5

What is one problem associated with using retroviruses as human gene therapy vectors?

Accepted Answer

Retroviruses integrate their genetic material into the host genome at random locations, which can disrupt normal gene function or activate oncogenes, potentially leading to detrimental mutations or cancer.

Question 6

Why are conditional knockout animals desirable?

Accepted Answer

Conditional knockout animals allow for the deletion of genes that are essential for development at specific stages or in specific tissues, avoiding the lethality that might occur if these genes were absent from the entire organism from conception. This specificity is not achievable with traditional knockout methods, which delete the gene in all cells of the organism from the beginning of its development.

Question 7

Knockin mice can be created using the Cre/loxP system.In this procedure, the loxP sites are used to

Accepted Answer

The loxP sites are used to delete the neomycin-resistance marker gene.

Question 8

Transgenic organisms are used to clarify which gene may be responsible for a mutant phenotype because

Accepted Answer

Transgenic organisms can help identify the gene responsible for a mutant phenotype by introducing a normal (wild-type) gene into an organism with a mutant phenotype. If the introduced gene corrects the phenotype, it suggests that the gene is responsible for the observed mutation. This is useful especially because individuals with a mutant phenotype might have mutations in multiple genes, and transgenesis helps pinpoint the specific gene(s) involved.

Question 9

Recombinant Ti plasmids allow for

Accepted Answer

Recombinant Ti plasmids are engineered versions of the naturally occurring Ti (tumor-inducing) plasmids found in Agrobacterium tumefaciens. They have been modified to remove the genes responsible for causing tumors in plants, while retaining the ability to transfer DNA into plant cells. This makes them useful tools in plant genetic engineering, where they are used to introduce new genes (transgenes) into plant cells, thereby creating genetically modified plants with desirable traits.

Question 10

After exposure to Agrobacterium tumefaciens bacteria containing both a recombinant T-DNA vector and a helper plasmid, new plants can be grown from single cells in the presence of herbicide.Without the herbicide,

Accepted Answer

The presence of herbicide in the growth medium is to select for cells that have been transformed with a T-DNA vector containing a gene for herbicide resistance. Without the herbicide, both transformed (those with the T-DNA vector) and nontransformed cells can grow, as the selective pressure (herbicide) that would normally kill the nontransformed cells is absent.

Question 11

To create transgenic mice, DNA is injected into

Accepted Answer

To create transgenic mice, DNA is typically injected into a pronucleus of a zygote, which allows for the integration of the foreign DNA into the mouse genome at an early stage of development.

Question 12

CRISPR sequences occur naturally as

Accepted Answer

CRISPR sequences are part of an adaptive immune system in bacteria and archaea, providing a form of acquired immunity against viruses and plasmids.

Question 13

How can transgenic organisms be used to identify transcriptional enhancers?

Accepted Answer

A reporter gene can be used to identify transcriptional enhancers by constructing it in such a way that its expression is controlled by a potential enhancer within a genomic DNA fragment. This allows researchers to determine if the enhancer can activate transcription of the reporter gene in the context of the organism's genome.

Question 14

Currently the two main vectors for delivery of therapeutic genes for human gene therapy are

Accepted Answer

AAV (Adeno-Associated Virus) and retroviruses are the two main vectors currently used for the delivery of therapeutic genes in human gene therapy due to their efficiency in gene delivery and their ability to integrate into the host genome for long-term expression.

Question 15

Transgenic animals made by pronuclear injection can be limited for studies of the links between genes and disease because

Accepted Answer

Transgenic animals made by pronuclear injection can be limited because the transgene allele must be dominant to the normal, endogenous allele for its effects to be observed, and some diseases are indeed caused by recessive mutations, making it difficult to model these diseases with this method.

Question 16

A scientist wants to determine whether a mutant phenotype is due to the loss of gene C or gene D, which are both deleted in a mutant fly with abnormal eyes.Mutant flies with transgenic gene C have wild-type eyes, whereas mutant flies with transgenic gene D have abnormal eyes.What can be concluded from these results?

Accepted Answer

Since introducing gene C back into the mutant flies restores the wild-type eye phenotype, it indicates that the loss of gene C is responsible for the abnormal eyes. The fact that reintroducing gene D does not correct the phenotype suggests that gene D is not directly involved in the development of normal eyes in this context.

Question 17

Pharming refers to the use of transgenic animals and plants to produce protein drugs, such as

Accepted Answer

Pharming involves producing pharmaceutical proteins in the milk, eggs, or blood of genetically modified animals, such as producing antithrombin III in goat milk, rather than using traditional cell cultures or bacteria.

Question 18

A trait unique to embryonic stem cells that makes them useful for generating knockout animals is that they

Accepted Answer

Embryonic stem cells are unique because they are totipotent, meaning they have the ability to develop into any type of cell in the organism, which is crucial for generating knockout animals.

Question 19

Although bacteria can be used to produce proteins for therapeutic uses, what can be a disadvantage to using a prokaryotic system?

Accepted Answer

Prokaryotic systems, such as bacteria, lack the cellular machinery for posttranslational modifications (e.g., glycosylation, phosphorylation) that are often necessary for the proper function of eukaryotic proteins. This can lead to the production of proteins that are not correctly processed, affecting their stability, activity, or localization.

Question 20

A researcher has a laboratory strain of flies that have loss-of-function mutations in both gene X and white.These flies are used as hosts for P element transformation: Embryos of the double mutant strain are injected with two plasmids, one containing a wild-type copy of the white gene (w⁺)and a wild-type copy of gene X, side-by-side within P element inverted repeats, and the other plasmid containing only the P element transposase gene.Transgenic offspring of the injected flies will

Accepted Answer

The P element transformation technique involves integrating a gene of interest (in this case, a wild-type copy of the white gene and gene X) into the fly's genome at random locations using the P element transposase. The transposase facilitates the integration of the DNA within the P element inverted repeats into the fly's genome. Since the injected plasmids contain a wild-type copy of the white gene, the offspring that successfully integrate this gene will have red eyes (correcting the white mutation), and also a wild-type copy of gene X, but these integrations occur at random locations, not specifically replacing the mutant copies.

Quiz 18: Manipulating the Genomes of Eukaryotes