Deck 16: Forward Genetics and Recombinant Dna Technology

Question 1

If a mutagenesis screen provides some number of alleles shown by complementation analysis to be in the same gene, which of the following is true?

A)These mutants can be used to identify the role of the gene in metabolism.
B)The gene being studied must be present in more than one copy per haploid genome.
C)The gene, in whole or in part, must be involved in transformation.
D)The gene must be highly conserved in evolution.
E)The gene must be involved in regulating a signal pathway.

Answer 1

A

Question 2

What kind of analysis is needed to determine whether two mutations are in the same gene or in different genes?

Answer 2

complementation

Question 3

Besides the obvious fact that chemical mutagens are dangerous to handle, another major disadvantage to their use is that __________.

A)most of these mutations are immediately lethal
B)most chemically induced changes are detectable only by sequencing
C)chemical mutagens activate transposons
D)two or more generations of further matings are required to isolate them
E)they alter all A-T and C-G base pairing

Answer 3

B

Question 4

To introduce dsRNA into C. elegans, it is enough just to dip the worms into media that includes E. coli containing the dsRNA because __________.

A)E. coli infect C. elegans and then the RNA is released
B)E. coli break up into pieces due to the presence of the worms
C)C. elegans feed on the transgenic bacteria
D)C. elegans emit toxins that paralyze the bacteria
E)E. coli emit chemicals that cause pores to open in the nematode body wall

Question 5

You have evidence that a gene, VTE4, of known sequence and well-understood transcriptional regulation, is available from another lab. The product of this gene enables seeds to produce a significantly increased amount of vitamin E from a substrate already produced in Brassica napus, the plant that gives us canola oil. To produce canola oil with increased vitamin E, how would you proceed?

A)Select Brassica plants with the highest titer of the vitamin, isolate the genes responsible, and cause these genes to duplicate.
B)Use a yeast system to engineer yeasts that produce the vitamin, and get manufacturers to add this to the canola oil during bottling.
C)Introduce the gene and necessary cis elements into Brassica, along with a reporter gene, then measure the vitamin E produced.
D)Clone VTE4 in A. tumefaciens and use these bacteria to produce transgenic Brassica.
E)Introduce VTE4 into tomato plants or another food that humans eat more than Brassica.

Question 6

If mutagenizing a number of Drosophila results in several observable phenotypes but also in several lethal mutations, does this mean that recessive lethal mutations cannot be studied further?

A)No-the lethal allele can be recovered from heterozygous siblings.
B)No-the lethal allele can be sequenced from the other embryos.
C)Yes-lethal alleles can be studied only if they are recessive.
D)Yes-lethal alleles can be studied only if they are conditional.
E)Yes-unless the lethal allele can be supplemented with a missing gene product.

Question 7

Before Muller's discovery that radiation induces mutation, scientists had to work on mutations that were found solely by phenotype differences in natural populations. Which of the features
Of Drosophila made it a fortuitous choice for Morgan and his colleagues?

A)having a long life cycle
B)especially high rate of mutation
C)large number of easily visible phenotypes
D)well-known biochemical pathways
E)the number of genes with only two alleles

Question 8

Enhancer trapping might occur if you create a library of insertions bearing enhancer-less GAL4 genes. Their expression will be controlled by __________.

A)also inserting a viral enhancer
B)also inserting a GAL4 reporter
C)including a bacterial origin sequence
D)enhancers mapping near the insertion site
E)including an enhancer activator

Question 9

Identifying an autosomal recessive mutation in a mutagenic screen in Drosophila requires identification of a mutant in the F₃ generation. If testing for a sex-linked recessive lethal mutation (e.g., cn l + using a balancer chromosome such as cnCyO), in which generation can lines with mutations be identified?

Question 10

If a gene in Drosophila is expressed only when an imaginal disc (A)begins to differentiate, it is referred to as a homeotic gene. Recessive mutations in such genes often result in loss of function so that the structure does not develop. If the gene is expressed, but in a different imaginal disc (B), what is the result?

A)loss of function of disc B's primary gene
B)gain of function of several inappropriate genes in disc A
C)gain of function in disc B at the "wrong" location
D)deregulation of gene expression throughout disc A
E)deregulation of gene expression throughout disc B

Question 11

Which of the following would make a human disorder-causing allele or gene easiest to locate?

A)a genomic library for the chromosome on which the gene is located
B)a cDNA library for the chromosome on which the gene is located
C)a group of 10 known candidate genes
D)a transposon known to segregate with the gene
E)a single patient with a chromosomal translocation associated with the gene

Question 12

Genes for regulatory elements, such as creb, were found to be important in animal learning. Which of the following would increase the probability that such an element is studied throughout the animal kingdom?

A)its unique sequence in Drosophila
B)the finding that creb is highly conserved
C)the number of repeats of the creb gene
D)the interaction of creb with cAMP
E)the finding that creb activates odor perception

Question 13

In a disease associated with a nucleotide repeat, anticipation is often noticed in subsequent generations, usually associated with a more severe phenotype. Which of the following is a more likely cause of anticipation?

A)The CAG alleles with a high number of repeats are unstable and change size from generation to generation.
B)Subtle phenotypic nuances are more often sought by a physician.
C)Family members are exposed to the same mutagens.
D)Highly repeated sequences are expressed more often.
E)The sequences have greater stability in later generations.

Question 14

In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers?

A)inversions
B)dominants
C)lethal recessive
D)inversions plus dominant
E)lethal plus inversions

Question 15

A researcher wants to mutagenize an organism. He is not in need of a large number of mutants but is more concerned with being able to find and then to amplify the mutated sequence. Which of the following would therefore be more useful?

A)ionizing radiation
B)UV radiation
C)transposon insertion
D)a chemical mutagen
E)search for spontaneous mutant

Question 16

The reasons for using transposon-based mutagenesis include all of the following except __________.

A)disrupting the coding sequence
B)disrupting a regulatory sequence
C)creating improper splice sequences
D)addition of alkyl groups to bases
E)blocking of enhancer-promoter interactions

Question 17

If you wish to rid an experimental organism of the function of a gene, you can use RNAi. What would you inject into the organism?

A)co-suppressor with double-stranded (ds)DNA
B)ssRNA complementary to cDNA
C)ssRNA complementary to mRNA
D)dsRNA homologous to the gene
E)dsRNA including transposase

Question 18

Conditional alleles result in phenotypic differences in permissive as opposed to restrictive conditions. What do these conditions have in common?

Question 19

EMS (ethylmethane sulfonate)is mutagenic because __________.

A)it breaks phosphodiester bonds
B)it adds alkyl groups to bases
C)it forms cross-links between DNA strands
D)it makes DNA more susceptible to radiation
E)it causes chromosomal deletions

Question 20

In reverse genetics, what is the correct order in which the experimenter proceeds?

A)silencing the genes in question using RNAi, followed by generating gain-of-function alleles
B)screening genes via PCR, followed by deletion of the flanking sequences
C)selection of a phenotypic alternative for the gene in question and sequencing its DNA
D)induction of and selection for a mutant allele with a known sequence, followed by screening for mutations of interest
E)random bombardment of the DNA with a known mutagen, followed by observation of offspring for newly acquired traits

Question 21

Knockout libraries are available already prepared for some organisms such as Drosophila. These libraries are originally made by what method?

Question 22

In nature, RNAi protects cells against infection by what kind of pathogen?

Question 23

Why do we so frequently use mutant alleles to determine structure and/or function of the wild type?

Question 24

For a contiguous sequence to be most useful in molecular mapping of a particular mutation, what should the contiguous sequence include?

Question 25

In a given situation, reduced or missing function in gene A results in a viable but noticeable phenotype. The same is true for gene B. However, when both gene A and gene B products are reduced or missing in the same organism, the result is lethality. What is this called?

Question 26

In positional cloning, the researcher begins with a phenotype. To move toward identification of its DNA sequence, she must begin with what step?

Question 27

In an organism, X, it is found to be impossible to generate loss-of-function mutants for most genes. There is an alternative method of introducing random mutations that can later be screened for the gene(s)in question. This can be accomplished by using insertions due to what structures?

Question 28

Why is only a fraction of an organism's genes represented in any cDNA library?

Question 29

A genetic strategy that starts with knowing the DNA sequence and works toward identifying an associated phenotype is known as ________.

Question 30

DNA markers that are found to segregate with a mutation of interest can be used to determine the mutation's distance from the markers by looking at what?

Question 31

The GFP gene is useful as a reporter gene because the cells and tissues with it emit bioluminescence when treated with what, which functions as a substrate?

Question 32

Suppose a mutagen is used on an inbred population of mice to establish cell lines, each including a different mutant allele, which can then be tested for function. This technique is known as ________.

Question 33

A balancer chromosome includes a recessive lethal allele, a marker dominant allele, and ________.

Question 34

In mapping the HD gene associated with Huntington disease, eventually researchers narrowed down their hunt to four candidate genes within the mapped region. How did they identify one of these as the definitive HD gene?

Question 35

You have performed a mutagenesis screening in a population of organisms. Describe how you would identify mutations that are dominant. Describe how you would identify mutations that are recessive.

Question 36

In the process of identifying mutations in animals, dominant mutations can be found after one generation of mating between the mutagenized male organism and wild-type female. To identify
the non-sex-linked (autosomal)recessive mutants requires ________ generations.

Question 37

If a mutagen such as EMS is used to produce numerous mutagenized cell lines for an organism, PCR can be used to select for a particular gene. However, what feature of this selected sequence is used to find the ones with mutations in that gene?

Question 38

Should we allow (or urge)testing of minor-age children or teens for adult-onset disorders for which there is no treatment or cure?

Question 39

If an experimenter wants to use the GFP method but needs to detect the presence or absence of several proteins at the same time, he can take advantage of mutational variants of GFP that emit what?

Question 40

Suppose a scientist wants to identify a gene in a particular plant species by transposon tagging, but he is initially stumped because he finds no active transposons. He hypothesizes, however, that he can introduce a transposon from another plant species. Why might this be possible?

Question 41

In TILLING, a population of inbred organisms is mutagenized to saturation. DNA from mutagenized lines is isolated and amplified by PCR. PCR products are denatured and allowed to reanneal and then treated with an endonuclease. Why is the denaturation/re-annealing step important for the detection of mutant alleles?

Question 42

Design an experiment that uses enhancer trapping to drive the expression of a gene of interest.

Question 43

Would it be possible and/or appropriate to design a genetic screen to look for a gene(s)involved in homosexuality?

Question 44

Transgenic fusions between a gene and a reporter are used to determine whether a gene is expressed. Which of these components allows the researcher to work with living specimens,
and why?