Q: Which of the following equations correctly represents the number of possible mutant animals needed if you want to generate conditional mutants for every gene in every tissue, given 39 tissues and 30,000 genes?

$$39 \times 30,000 = 1,170,000$$

Question 1

Which of the following best explains why a traditional knockout of a gene critical for development often results in embryonic lethality?

Accepted Answer

The gene is essential for early developmental processes, so its complete loss prevents the embryo from developing properly.

Question 2

What is the primary advantage of using the Cre-loxP system to generate conditional knockouts in mice?

Accepted Answer

It allows for tissue-specific or time-specific deletion of a gene, avoiding embryonic lethality.

Question 3

A researcher wants to study the function of GeneX in the liver but not in other tissues. Which mouse lines should be crossed to achieve a liver-specific knockout of GeneX using the Cre-loxP system?

Accepted Answer

A mouse expressing Cre under a liver-specific promoter crossed with a mouse homozygous for a floxed GeneX allele.

Question 4

Which of the following best describes the molecular mechanism of Cre recombinase in the Cre-loxP system?

Accepted Answer

Cre recombinase catalyzes site-specific recombination between two loxP sites, excising the DNA sequence between them.

Question 5

Why is it not feasible to generate conditional mutant lines for every single gene and tissue combination in mice?

Accepted Answer

The number of possible combinations is extremely large, requiring over a million mutant animals and years of work.

Question 6

In a Cre-loxP experiment, a mouse with a floxed allele of GeneX is injected with AAV-Cre virus specifically into the hippocampus. What is the expected outcome?

Accepted Answer

GeneX will be deleted only in the hippocampus, leaving other tissues unaffected.

Question 7

Which behavioral change was observed in mice with hippocampal CREB deletion?

Accepted Answer

Decreased depressive and anxiety-like behaviors, such as reduced immobility in the forced swim test.

Question 8

What is the function of the EGFP-L10a fusion protein in the TRAP-seq technique?

Accepted Answer

It tags ribosomes in specific cell types, allowing for the isolation of actively translating mRNAs from those cells.

Question 9

A mouse line is engineered with a stop cassette flanked by loxP sites upstream of a reporter gene. What happens when Cre recombinase is expressed in a specific tissue?

Accepted Answer

The stop cassette is excised, allowing reporter gene expression only in that tissue.

Question 10

Which of the following equations correctly represents the number of possible mutant animals needed if you want to generate conditional mutants for every gene in every tissue, given 39 tissues and 30,000 genes?

Accepted Answer

$$39 	imes 30,000 = 1,170,000$$

Question 11

In the context of the Cre-loxP system, what does the term 'floxed' refer to?

Accepted Answer

A gene or DNA sequence flanked by loxP sites.

Question 12

A scientist observes that deletion of CREB in the hippocampus leads to increased neurogenesis. Which experimental approach would best allow them to identify changes in gene expression specifically in hippocampal neurons?

Accepted Answer

Use TRAP-seq with EGFP-L10a expressed under a neuron-specific Cre driver.

Question 13

Which of the following is a limitation of using the Cre-loxP system for generating conditional knockouts?

Accepted Answer

It requires the availability of tissue-specific Cre driver lines, which may not exist for all tissues.

Question 14

If a mouse is homozygous for a floxed allele but does not express Cre recombinase, what is the expected phenotype?

Accepted Answer

The mouse will express the gene normally, as no recombination occurs.

Question 15

Which of the following best describes the purpose of using a control mouse that is homozygous for loxP sites but does not express Cre recombinase?

Accepted Answer

To ensure that the presence of loxP sites alone does not affect gene function or phenotype.

Question 16

A researcher uses a Pet-cre mouse line to drive EGFP-L10a expression in the dorsal raphe. What is the likely outcome?

Accepted Answer

EGFP-L10a will be expressed specifically in serotonergic neurons of the dorsal raphe.

Question 17

Which of the following is a real-world application of genetic engineering mentioned in the study materials?

Accepted Answer

Producing human insulin using genetically modified organisms.

Question 18

In a TRAP-seq experiment, what is the role of the anti-EGFP antibody?

Accepted Answer

It binds to EGFP-L10a-tagged ribosomes, allowing their isolation from cell lysates.

Question 19

Which neurotransmitter systems are targeted by antidepressants and are affected in the hippocampus during chronic stress?

Accepted Answer

Serotonin, dopamine, and norepinephrine systems.

Conditional Mutants, Cre-LoxP System, and Genetic Engineering in Mouse Models

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