GRE Subject Test: Biology : Genetics, DNA, and Molecular Biology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Prokaryotic Inheritance

Which recombinant process depends on a F factor plasmid?

Possible Answers:

Transformation

Translocation

Transduction

Conjugation

Correct answer:

Conjugation

Explanation:

Beginning the process of conjugation requires the trait encoded by the F (fertility) plasmid. Transformation is the uptake of naked DNA, transduction is the transfer of genetic material via a virus, and translocation is the movement of a ribosome during protein translation.

Example Question #2 : Understanding Prokaryotic Inheritance

What type of prokaryotic genetic recombination requires the presence of plasmids?

Possible Answers:

Binary fission

Transformation

Transduction

Conjugation

Correct answer:

Conjugation

Explanation:

Conjugation is a type of genetic recombination that requires one bacterium to have the F-plasmid in order to create a sex pilus. This sex pilus will connect with another bacterium and allow DNA to pass between the bacteria.

Transduction is the transfer of genetic information to a bacterium via a vector, such as a bacteriophage. Transformation occurs when a bacterial cell receives genetic material from its surrounding environment. Binary fission does not involve recombination, and is the term for bacterial cell division that results in two identical offspring from a single parental cell.

Example Question #21 : Microbiology

Which of the following is false about conjugation?

I. It is a form of sexual reproduction

II. It forms a bridge between two bacterial cells; the bridge is called a plasmid

III. It involves transport of genetic material via vectors

Possible Answers:

II and III

I and II

I only

II only

Correct answer:

II and III

Explanation:

Bacterial cells are capable of conjugation, a form of sexual reproduction. The process involves the formation of a bridge between bacterial cells that facilitates the movement of genetic material from one cell to the other. This bridge is called a sex pilus. A plasmid is a circular extrachromosomal DNA fragment. To initiate conjugation, a bacterium must possess a plasmid that enables formation of the sex pilus.

Bacterial cells can also exchange genetic material indirectly via viral vectors (certain bacteriophages) that carry bacterial genetic information from one cell to another; however, this does not occur in conjugation. It occurs in another form of sexual reproduction called transduction.

Example Question #981 : Mcat Biological Sciences

A bacterial cell must possess a __________ gene on the __________ in order to initiate conjugation.

Possible Answers:

plasmid . . . sex pilus

sex pilus . . . plasmid

plasmid . . . nucleoid

sex pilus . . . nucleoid

Correct answer:

sex pilus . . . plasmid

Explanation:

Conjugation is a form of sexual reproduction in bacterial cells. It involves formation of a bridge, called the sex pilus, between two bacterial cells. After sex pilus formation, the donor cell will pass genetic information to the recipient cell via the sex pilus. In order to initiate conjugation, a bacterial cell must contain the genes that code for the sex pilus, which are usually found on a specific plasmid. Recall that a plasmid contains the extrachromosomal DNA (found outside the bacterial cells’ chromosomes), whereas the nucleoid contains the chromosomal DNA. Sex pilus genes are always found on the plasmid, and can be passed from one cell to another during conjugation. This exchange increases the number of cells capable of forming the sex pilus, increasing the ability for bacterial cells to perform sexual reproduction and increase genetic variation.

Example Question #3 : Understanding Prokaryotic Inheritance

Which of the following is true of both bacterial conjugation and meiosis?

Possible Answers:

Both processes produce four haploid cells

Both processes involve genetic recombination

Both processes are a form of asexual reproduction

Bacterial conjugation is a form of sexual reproduction, whereas meiosis is a form of asexual reproduction

Correct answer:

Both processes involve genetic recombination

Explanation:

The only similarity between conjugation and meiosis is that both processes are types of sexual reproduction. Remember that sexual reproduction is characterized by the presence of genetic recombination (the ability to exchange genetic material between two DNA molecules). The result of both processes are daughter cells that are genetically unique from the parent cells.

In meiosis, genetic recombination occurs during crossing over in prophase I. In conjugation, genetic recombination occurs when the DNA from the donor bacterial cell is incorporated into the recipient bacterial cell. Only meiosis produces four daughter cells; conjugation produces only two.

Example Question #961 : Biology

What is the structure in prokaryotic cells that often holds antibiotic resistance genes?

Possible Answers:

Nucleus

Nuclear area

Plasmid

Prophage

Nucleoid

Correct answer:

Plasmid

Explanation:

Antibiotic resistance genes are often found on plasmids, which are small DNA molecules which are easily transfered to other prokaryotic cells.

Example Question #28 : Microbiology

In a small village, a doctor over-prescribed Ciprofloxin (an antiobiotic) to his patients. The result was that the majority of his patients had developed a new strain of bacteria that had become resistant to Ciprofloxin. 

What is a possible route that may have caused these bacteria to become antibiotic resistant?

Possible Answers:

The antibiotic resistant bacteria had the ability to degrade the antibiotic in their lysosomes

The bacteria learned to metabolize the antibiotic

The antibiotic lost its potency

An antibiotic resistant gene was passed on through the plasmids in a group of antibiotic resistant bacteria

The bacteria developed a way to prevent the antibiotic from entering into their cells

Correct answer:

An antibiotic resistant gene was passed on through the plasmids in a group of antibiotic resistant bacteria

Explanation:

Antibiotic resistant genes are commonly transferred through plasmids. Plasmids are small, circular, extra-chromosomal pieces of DNA that contain supplemental genes, which can be passed from bacteria to bacteria.

Example Question #29 : Microbiology

Which of the following characteristics make plasmid DNA useful for researchers?

Possible Answers:

Readily incorporate cloned DNA

Capable of being isolated from genomic DNA 

Capable of autonomous replication

All of the answers

Correct answer:

All of the answers

Explanation:

Plasmids are phenomenally useful for a number of reasons. They are capable of autonomous replication inside a suitable host (such as simple prokaryotes). Because they are non-genomic DNA (not located in the nucleus), plasmids are easily isolated and separated from the host's DNA. It is also relatively easy to insert cloned DNA into plasmid vectors. This allows for expression of recombinant proteins in prokaryotic cells.

Example Question #961 : Biology

Which of the following is false regarding plasmids?

Possible Answers:

A plasmid is a single-stranded DNA molecule found outside the nucleoid

Plasmids can contain genes that code for the sex pilus

Plasmids may provide antibiotic resistance

A plasmid is a circular DNA molecule

Correct answer:

A plasmid is a single-stranded DNA molecule found outside the nucleoid

Explanation:

Plasmids are circular, double-stranded DNA molecules found outside the nucleoid (extrachomosomal DNA). They can serve a variety of functions and code for traits that may vary within a single species, since different individuals may carry different plasmids.

Most notable are the plasmids related to antibiotic resistance and plasmids required for formation of the sex pilus in conjugation. Recall that antibiotic resistance is the ability of a bacterial cell to survive in the presence of antibiotics. This ability is facilitated by antibiotic resistant proteins that are coded by certain genes found on the plasmid of a bacterial cell.

Example Question #962 : Biology

Viruses can infect host cells by incorporating themselves into the host cell’s genome. Based on this information, what will you most likely find in a virus?

Possible Answers:

Plasmids because they contain genes for antibiotic resistance

Plasmids because they can integrate with chromosomes

Episomes because they contain genes for antibiotic resistance

Episomes because they can integrate with chromosomes

Correct answer:

Episomes because they can integrate with chromosomes

Explanation:

The question states that a virus infects a host cell by integrating with the host cell’s genome; therefore, the virus integrates with the chromosomes inside the nucleus of the host cell. Recall that both plasmids and episomes are extrachromosomal DNA molecules (DNA molecules found outside the chromosomes), however, only episomes can integrate with the chromosomes inside the nucleus of a host cell. This means that a virus will only be able to infect host cells if it contains an episome. Plasmids are only found in bacteria and cannot integrate with chromosomal DNA.

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