GRE Subject Test: Biology : Understanding Polymorphisms

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

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Example Questions

Example Question #1 : Understanding Polymorphisms

What term best describes when one species exhibits two or more defined phenotypes within the same population?

Possible Answers:

Sympatry 

Allopatry 

Polymorphism

Assortative mating

Natural selection

Correct answer:

Polymorphism

Explanation:

The correct answer is polymorphism. A polymorphism refers to multiple phenoytpes (morphs) that exist within a population, generally as a result of multiple alleles for the same gene.

Sympatry and allopatry refer to mechanisms of speciation and natural selection favors a certain phenotype for its fitness or other survival advantages. Assortative mating describes a biased mating pattern based on either phenotype or behavior. 

Example Question #2 : Understanding Polymorphisms

Which of the following is most accurate about single nucleotide polymorphisms (SNPs)?

Possible Answers:

SNPs occur in only non-coding regions

SNPs are more frequently found in AT-rich microsatellite regions

SNPs occur in only coding regions

None of these

SNPs occur in 1% or more of the population 

Correct answer:

SNPs occur in 1% or more of the population 

Explanation:

In order for a nucleotide substitution to be considered a SNP and not a random mutation, it must occur in 1% or more of the population. SNPs are more frequently found in non-coding regions. Typically, SNPs are much less commonly found in AT-rich microsatellites. 

Example Question #3 : Understanding Polymorphisms

What is the major difference between synonymous and non-synonymous substitutions?

Possible Answers:

Synonymous substitutions result in missense mutations, non-synonymous substitutions result in nonsense mutations

Synonymous substitutions do not result in an amino acid change in the protein, but non-synonymous substitutions do

Non-synonymous substitutions result in missense mutations, synonymous substitutions result in nonsense mutations

None of these

Non-synonymous substitutions do not result in an amino acid change in the protein, but synonymous substitutions do

Correct answer:

Synonymous substitutions do not result in an amino acid change in the protein, but non-synonymous substitutions do

Explanation:

If single nucleotide polymorphisms (SNPs) that occur in coding regions do not trigger an amino acid change in the protein, they are synonymous. A SNP can cause a missense mutation (an amino acid change in the protein) or a nonsense mutation (an amino acid change to a stop codon), both of these are nonsynonymous substitutions.  

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