Evolution Quiz

Point mutation

A change affecting a single DNA position, including a single-base substitution, insertion, or deletion.

Substitution

A mutation in which one nucleotide replaces another, so the sequence length stays the same.

Purine

A nitrogenous base in the A or G group. Adenine and guanine are purines.

Pyrimidine

A nitrogenous base in the C, T, or U group. DNA uses C and T, while RNA uses C and U.

Transition

A substitution within the same base class, such as A to G or C to T.

Transversion

A substitution between base classes, such as a purine replaced by a pyrimidine or vice versa.

Indel

An insertion or deletion of one or more nucleotides.

Frameshift mutation

An insertion or deletion in a coding sequence that adds or removes a number of bases not divisible by three, changing how downstream bases are grouped into codons.

In-frame insertion or deletion

An insertion or deletion in a coding sequence that adds or removes a multiple of three bases, preserving the downstream reading frame.

Silent mutation

A coding substitution that changes a codon while preserving the amino acid it specifies.

Synonymous substitution

A nucleotide substitution that changes a codon to another codon for the same amino acid. Also called a silent mutation in this context.

Missense mutation

A substitution that changes a codon to one that specifies a different amino acid.

Nonsense mutation

A substitution that changes an amino-acid codon into a stop codon.

Nonsynonymous substitution

A coding substitution that changes what a codon specifies, including missense and nonsense substitutions.

Codon

A sequence of three mRNA bases that specifies an amino acid or a stop signal.

Reading frame

The way a nucleotide sequence is grouped into consecutive three-base codons from a specified starting point.

Start codon

The standard start codon, AUG, which also specifies methionine.

Stop codons

The codons UAA, UAG, and UGA, which signal the end of translation.

Chromosomal rearrangement

A structural change involving a chromosome segment, such as a deletion, duplication, insertion, inversion, or translocation.

Chromosomal deletion

The loss of a chromosome segment.

Chromosomal duplication

The presence of an extra copy of a chromosome segment.

Chromosomal inversion

A chromosome segment that breaks and rejoins in the opposite orientation.

Pericentric inversion

An inversion that includes the centromere.

Paracentric inversion

An inversion that excludes the centromere and occurs within one chromosome arm.

Chromosomal translocation

The relocation of a chromosome segment, commonly to a nonhomologous chromosome.

Reciprocal translocation

An exchange of segments between two nonhomologous chromosomes.

Transposition

The movement or copying of a transposable DNA element to a new genomic location.

Transposable element

A DNA sequence that can move or be copied to another genomic location. Also called a transposon.

Unequal crossing-over

Crossing-over between misaligned homologous chromosomes, producing one chromosome with a duplicated segment and another with a deletion.

Inversion loop

A loop that forms during meiosis when an inverted chromosome pairs with a homolog that has the standard orientation.