GRE Subject Test: Biology › Understanding Polymorphisms
What term best describes when one species exhibits two or more defined phenotypes within the same population?
Polymorphism
Sympatry
Allopatry
Natural selection
Assortative mating
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.
Which of the following is most accurate about single nucleotide polymorphisms (SNPs)?
SNPs occur in 1% or more of the population
SNPs occur in only non-coding regions
SNPs occur in only coding regions
SNPs are more frequently found in AT-rich microsatellite regions
None of these
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.
What is the major difference between synonymous and non-synonymous substitutions?
Synonymous substitutions do not result in an amino acid change in the protein, but non-synonymous substitutions do
Non-synonymous substitutions do not result in an amino acid change in the protein, but synonymous substitutions do
Synonymous substitutions result in missense mutations, non-synonymous substitutions result in nonsense mutations
Non-synonymous substitutions result in missense mutations, synonymous substitutions result in nonsense mutations
None of these
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.