Evolution Quiz

Point mutation A change affecting a single DNA position. In your readings, this includes a single-base substitution, insertion, or deletion.

Substitution A mutation in which one nucleotide replaces another. 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. In DNA, A ↔ G and C ↔ T are transitions.

Transversion A substitution between base classes. In DNA, an A or G is replaced by a C or T, 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 that is not divisible by three. This changes 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. The downstream reading frame is preserved.

Silent mutation A coding substitution that changes a codon while preserving the amino acid. Example: mRNA GAA → GAG, both of which specify glutamate.

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. Example: mRNA GAA → GAC changes glutamate to aspartate.

Nonsense mutation A substitution that changes an amino-acid codon into a stop codon. Example: mRNA CAA → UAA changes glutamine to stop.

Nonsynonymous substitution A coding substitution that changes what a codon specifies. Missense and nonsense substitutions are examples.

Two ways to classify a coding substitution Transition or transversion describes the base change. Silent, missense, or nonsense describes the codon effect. Example: coding DNA CAA → TAA is both a transition and a nonsense mutation.

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.

Coding DNA to mRNA When the coding DNA strand is written 5′ → 3′, replace T with U. Example: 5′-TGG-3′ becomes 5′-UGG-3′.

Template DNA to mRNA Make the complementary RNA sequence antiparallel to the DNA template. Example: template 3′-ACC-5′ gives mRNA 5′-UGG-3′.

How to use a codon table Read the mRNA codon 5′ → 3′. On a common grid, locate the first base on the left, the second across the top, and the third on the right. On a wheel, read from the center outward.

Start codon AUG is the standard start codon and also specifies methionine.

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

Chromosomal rearrangement A structural change involving a chromosome segment. Examples include deletions, duplications, insertions, inversions, and translocations.

Chromosomal deletion The loss of a chromosome segment.

Chromosomal duplication The presence of an extra copy of a chromosome segment.

Chromosomal insertion The addition of a DNA segment at a chromosome site.

Chromosomal inversion A chromosome segment 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. One resulting chromosome can carry a duplicated segment while the other carries a deletion.

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