25
Dec
2009
admin

Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

N

N
(1) In DNA or RNA, an unknown nucleotide. (2) In proteins, asparagine.
N-terminal
(see amino terminal)
natural selection (selection)
Differential reproduction of different members of a species due to the variability in fitness among individuals or genotypes, leading to changes in allele frequencies over time.
NCBI
National Center for Biotechnological Information.
negative selection
(see purifying selection)
neighbor-joining
An algorithm for constructing phylogenetic trees using distance data.
neutral theory (neutral-mutation theory or neutral-mutation hypothesis)
The proposal that evolution at the molecular level is primarily determined by mutational input and random genetic drift, rather than by natural selection.
NNI
Nearest Neighbor Interchange.
node
The graphical representation in a phylogenetic tree of an extant or ancestral operational taxonomic unit.
nondegenerate site
A nucleotide site in the coding region at which all substitutions are nonsynonymous.
nondisjunction
The failure of homologous chromosomes to separate during meiosis.
nonfunctionalization (silencing)
The turning of a functional gene into a pseudogene following the occurrence of an incapacitating mutation.
nongenic DNA
The portion of the genome that does not contain genes.
nonsense codon
(see termination codon)
nonsense strand
The transcribed strand of a gene, the sequence of which is complementary to the RNA transcript.
nonsynonymous substitution (missense substitution)
A substitution that alters a codon to that for another amino acid.
nucleotide (base)
A molecule composed of a nitrogen base, a sugar, and a phosphate group. Any of the basic building blocks of nucleic acids.
nucleotide diversity
A measure of polymorphism applied to nucleic acid sequences. The mean number of nucleotide differences per site between any two randomly chosen sequences from a population.
nucleotide substitution
A mutation in which one nucleotide is substituted for another. In evolution, the substitution of a nucleotide by another nucleotide that becomes fixed in a population.
nucleotypic
Referring to a function of a DNA sequence other than as a carrier of genetic information (e.g., serving as a skeleton for the nucleus).
nucleus (plural, nuclei)
A membrane-enclosed organelle containing the chromosomes in eukaryotes.