GRE Subject Test: Biology : Genetic Regulation

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

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Example Questions

Example Question #1 : Genetic Regulation

Which of the following is not an example of an epigenetic cause of trait variation? 

Possible Answers:

DNA methylation

X-chromosome inactivation 

Different exon sequences

Imprinting

Histone acetytlation 

Correct answer:

Different exon sequences

Explanation:

Epigenetics are changes to the genome that result in phenotypic variation that have nothing to do with changes in the actual DNA sequence. All listed answers occur independently of DNA sequence, except for "different exon sequences," which is the actual sequence of an exon. This referces to alternative splicing, an is not related to the modification of DNA or histones.

Example Question #61 : Genetics, Dna, And Molecular Biology

Which of the following is true about the effects of epigenetics on gene expression? 

Possible Answers:

None of the other answers 

Modification of histone arginine residues alters gene expression by changing the affinity between DNA and histones

Modification of chromatin lysine residues alters gene expression by changing the affinity between DNA and chromatin

Modification of nucleosome lysine residues alters gene expression by changing the affinity between DNA and histones

Modification of histone lysine residues alters gene expression by changing the affinity between DNA and histones

Correct answer:

Modification of histone lysine residues alters gene expression by changing the affinity between DNA and histones

Explanation:

Methylation and acetylation of histones occurs on lysine residues, thereby decreasing or increasing gene expression, respectively. Methylation increases the affinity for histones and DNA, where acetylation decreases the affinity for histones and DNA. Gene expression is in part controlled by modification of histone proteins, rather non-histone chromosomal proteins. 

Example Question #1 : Understanding Epigenetics

In terms of epigenetics, acetylated histones usually result in which of the following?

Possible Answers:

Increase in transcription/ gene expression

Decrease in DNA - lamina association 

Decrease in transcription/ gene expression

Increase in DNA - lamina association

Production and assembly of ribosomes

Correct answer:

Increase in transcription/ gene expression

Explanation:

The correct answer is an increase in gene expression. Histone acetylation removes positive charges on the histones, reducing the affinity of DNA for histones. Remember that DNA is negatively charged due to the phosphate groups on its backbone. DNA and histones are attracted to each other because histones are positively charged due to being rich in basic amino acid residues. Acetylation relaxes the tightly bound DNA allowing transcription factors to bind promoter regions. DNA deacetylation and methylation supress gene transcription by making DNA and histones associate more tightly together, decreasing the ability of transcription factors and/or RNA polymerase to bind the DNA. Histone modifications such as acetylation, deacetylation, and methylation do not directly affect the amount of DNA. If a histone is acetylated on a part of the DNA which codes for the genes for ribosome production, then an increase in ribosomal production and assembly could occur, but genes coding for ribosomes are greatly outnumbered by other genes, and thus, this is not the usual result of acetylating histones. 

Example Question #1 : Understanding Oncogenes

Which of the following choices could activate a proto-oncogene?

Possible Answers:

Exposure to mutagens

Chromosomal translocations

Gene duplication

Any of these could activate a proto-oncogene

Correct answer:

Any of these could activate a proto-oncogene

Explanation:

Proto-oncogenes are genes that have the ability to become oncogenes (genes that cause cancer). There are many ways to activate proto-oncogenes. Gene duplication can cause an increase in the expression of a particular protein, which can lead to cancer. Exposure to mutagens can cause a mutation on a proto-oncogene, which causes it to become activated. Chromosomal translocations can relocate proto-oncogenes to areas where they are expressed more rapidly. Most proto-oncogenes are involved in cell cycle regulation. Irregular expression of these genes can allow the cell to progress through the cell cycle too rapidly, resulting in unregulated cell division and tumor formation.

Example Question #62 : Genetics, Dna, And Molecular Biology

Which of the following best describes an oncogene?

Possible Answers:

A gene that causes uncontrollable growth

A gene that regulates cell growth

A gene that no longer makes a viable protein

A gene that stimulates apoptosis in cells

Correct answer:

A gene that causes uncontrollable growth

Explanation:

Oncogenes can be thought of as cancerous genes, or rather a gene that has the potential to cause cancer. They typically occur when a normal proto-oncogene undergoes a mutation. Proto-oncogenes normally code for growth and development in cells, and tightly regulate these processes. If mutated, these newly cancerous genes can stimulate unregulated growth, a symptom characteristic of cancerous cells.

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