Question 1

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?

Accepted Answer

F<sub>2</sub>

Question 2

A researcher is interested in testing the role for a highly- conserved amino acid in the function of a mouse protein. She has been unable to locate any pre- existing variants in this codon among a large number of available mouse strains. What might be her approach to generating such mutants?

Accepted Answer

Using CRISPR-Cas9 allows for precise editing of the DNA sequence at the specific codon of interest, enabling the generation of targeted mutations to study the function of the highly-conserved amino acid.

Question 3

In order to identify genes that function together in genetic pathways researchers can perform modifier screens, looking for second site enhancers or suppressors of a mutant. Which of the following is the most reasonable strategy for carrying out a suppressor screen in particular?

Accepted Answer

Suppressor screens involve mutagenizing an organism with a known mutation and then looking for secondary mutations that alleviate the phenotype of the original mutation. This approach helps identify genes that interact with or suppress the function of the gene containing the original mutation.

Question 4

A mutagenesis screen provides 24 alleles shown by complementation analysis to be in the same gene, which of the following is true?

Accepted Answer

These mutants can be used in various experiments to determine the function of the gene, such as observing the phenotypes associated with each mutant allele and comparing them to the wild type. This approach is a fundamental aspect of genetic analysis.

Question 5

If you wish to use RNAi to reduce the expression of a gene in an organism. What would you inject into the organism?

Accepted Answer

dsRNA homologous to the gene is used in RNA interference (RNAi) to reduce the expression of a specific gene. When introduced into the organism, the dsRNA is processed into small interfering RNAs (siRNAs) by the enzyme Dicer. These siRNAs then guide the RNA-induced silencing complex (RISC) to the target mRNA, leading to its degradation and thus reducing gene expression.

Question 6

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?

Accepted Answer

The finding that creb is highly conserved across different species would increase the likelihood of it being studied throughout the animal kingdom, as this suggests it plays a fundamental role in biological processes that are common across various animals.

Question 7

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

Accepted Answer

C. elegans feed on the transgenic bacteria, which allows for the introduction of dsRNA into the organism. This method is commonly used in RNA interference (RNAi) experiments.

Question 8

Which of the following tools/techniques would allow a researcher to measure the expression of a gene of interest in live organisms?

Accepted Answer

The answer of Which of the following tools/techniques would allow...

Question 9

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

Accepted Answer

The answer of What kind of analysis is needed to...

Question 10

EMS (ethylmethane sulfonate) is mutagenic because .

Accepted Answer

EMS (ethylmethane sulfonate) is mutagenic primarily because it adds alkyl groups to bases in DNA, leading to mispairing and mutations during DNA replication.

Question 11

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

Accepted Answer

Reverse genetics starts with a gene of interest and then investigates the function of that gene by analyzing the phenotypes resulting from specific mutations in the gene.

Question 12

Which portion of a gene might you target with the CRISPR- cas system to interfere with splicing?

Accepted Answer

The answer of Which portion of a gene might you...

Question 13

If a gene in Drosophila is expressed only in imaginal disc (A) when it 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 a transgenic organism is made in which the gene is expressed in a different imaginal, disc (B), what is the predicted result?

Accepted Answer

Homeotic genes specify the identity of body parts during development. When a homeotic gene from one imaginal disc is expressed in a different disc, it can cause the second disc to develop structures characteristic of the first disc's identity, leading to a gain of function of those structures in the second disc.

Question 14

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?

Accepted Answer

Alleles with a large number of repeats are unstable and tend to increase in size through generations, leading to earlier onset and more severe manifestations of the disease, a phenomenon known as anticipation.

Question 15

A gene, VTE4, from the sunflower of known sequence and well- understood transcriptional regulation, is available from another lab. The product of this gene enables sunflowers to to produce a significantly increased amount of vitamin E from a substrate produced in all plants. The plant Brassica napus is harvested for canola oil. To produce canola oil with increased vitamin E, how would you proceed?

Accepted Answer

The answer of A gene, VTE4, from the sunflower of...

Question 16

Before Muller's discovery that radiation induces mutation, scientists had to work on spontaneous mutants 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?

Accepted Answer

Drosophila was a fortuitous choice for Morgan and his colleagues primarily because it has a large number of visible phenotypes, which made it easier to identify and study genetic variations and mutations.

Question 17

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

Accepted Answer

Transposon-based mutagenesis typically causes significant disruptions in gene function, often resulting in dramatic mutations or null alleles, rather than minimal effects.

Question 18

A researcher wants to mutagenize an organism. She 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?

Accepted Answer

Transposon insertion is more useful for the researcher's needs because it allows for the easy identification and amplification of the mutated sequence. Transposons, or "jumping genes," can insert themselves into various locations within the genome. This insertion can disrupt or modify the function of genes at the insertion site. The presence of transposon sequences can be used as a molecular tag to identify and amplify the mutated gene, facilitating the study of the gene's function.

Question 19

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

Accepted Answer

Most chemically induced changes are subtle and not easily observable, requiring genetic mapping and sequencing to detect them.

Question 20

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?

Accepted Answer

Inversions are necessary and sufficient to suppress crossovers in Drosophila because they rearrange the genetic material in such a way that crossover events between the inverted segments and their homologous sequences in a non-inverted chromosome can lead to non-viable gametes, effectively preventing recombination within these regions.

Quiz 14: Regulation of Gene Expression in Eukaryotes