narrow sense heritability (HN)
The amount of individual phenotypic variation that is due to additive genetic variation.

native species
A species that was not introduced and historically, or currently, occurs in a given ecosystem.

natural catastrophes
Natural events causing great damage to populations and that increase their probability of extinction.

natural selection
Differential contribution of genotypes to the next generation due to differences in survival and reproduction.

NCA
Nested clade analysis. A statistical approach to describe how genetic variation is distributed spatially within a species’ geographic range. This method uses a haplotype tree to define a nested series of branches (clades), thereby allowing a nested analysis of the spatial distribution of genetic variation, often with the goal of resolving between past fragmentation, colonization, or range expansion events.

nearly exact test
A method of using a nearly exact P-value to test if the observed test statistic deviates from the expected value under the null hypothesis, For example, a test of whether populations are in Hardy–Weinberg proportions by comparing the observed chi-squared value to the chi-squared values of random computer permutations of genotypes from the population’s allele frequencies.

neighborhood
The area in a continuously distributed population that call be considered panmictic.

neutral allele
An allele that is not under selection because it does not affect fitness.

NMFS
National Marine Fisheries Service.

NOAA
National Oceanic Atmospheric Administration.

node
A branching point or end point on a phylogenic tree that represents either an ancestral taxon (internal node) or an extant taxon (external node).

nonindigenous species
Species present in a given ecosystem that were introduced and did not historically occur in that ecosystem.

nuclear DNA (nDNA)
DNA that forms chromosomes in the cell nucleus of eukaryotes.

nuclear gene
A gene located on a chromosome in the nucleus of a eukaryotic cell.

nucleotides
The building blocks of DNA and RNA made up of a nitrogen-containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.

null allele
An allele that is not detectable either due to a failure to produce a functional product or a mutation in a primer site that precludes amplification during PCR analysis.