A measure of genetic association between individuals relative to a reference biological population. Simple pedigree values assume specified inheritance and mating patterns; relatedness relevant to selection is not merely the fraction of genes two individuals share.

The folded site frequency spectrum counts variable sites by the less frequent allele count, without identifying which allele is ancestral. With four sampled sequences, counts one and three both contribute to the $3:1$ class, whereas count two gives the $2:2$ class.

Nonrandom distribution of genetic variation among biological populations, shaped by ancestry, movement, reproduction and drift.

For example, an allele can be common in one ancestry group and rare in another even without a causal effect on a measured trait. If trait prevalence also differs between groups, a pooled association can reflect ancestry. Modelling structure helps distinguish that source of association from a locus-specific effect. ^[ref]

Conservation genetics applies genetic evidence to maintaining biodiversity and viable biological populations. Measures of diversity, inbreeding and gene flow can identify isolation or help evaluate a proposed genetic rescue. Low diversity alone does not identify every ecological threat; demographic and habitat information remain necessary. In the Florida panther case, genetic and survival measurements together were used to assess restoration rather than treating introduced ancestry alone as proof of success. ^[ref]

The sex ratio is the relative abundance of sex classes in a specified biological population or life stage. It can be expressed as a ratio or as a fraction, so the convention and denominator must be stated. A birth sex ratio can differ from the adult or breeding sex ratio through unequal survival or participation in reproduction. This matters for population genetics because the number of successful breeders can differ from the total census size. ^[ref]

A comparison of nonsynonymous and synonymous polymorphism and divergence. Under a simple neutral model their ratios match. An excess of nonsynonymous divergence can support adaptive fixation, but mildly deleterious polymorphism, changing demography and site-class assumptions affect interpretation.^[ref]

The counts or proportions of segregating variants at different sample frequencies. Unfolded spectra use an inferred ancestral state; folded spectra use minor-allele counts.

An allele changes in frequency because of association with another selected allele. Recombination can weaken that association, so the response differs between linked and freely recombining backgrounds.

The Cossee-Arlman mechanism propagates a polymer through alkene coordination followed by insertion into a metal–carbon bond. Repetition extends the metal-bound chain. Regioselectivity controls monomer connectivity; it does not by itself specify tacticity.

Formation of a polymer by opening cyclic monomers and linking the resulting units. The repeat-unit inventory can be retained without eliminating a small molecule in each propagation step.

A chemical event preventing further growth of a polymer chain. Monofunctional end-capping units can reduce attainable chain length in a condensation system.

The number of reactive connections available on a monomer under a specified polymerization chemistry. One-functional units can terminate chains, two-functional units can build chains, and higher functionality can produce branching and networks.

An overdamped bead-spring model of polymer dynamics with local friction and no long-range hydrodynamic interaction. For an ideal unentangled chain of $N$ identical frictional units, the centre-of-mass diffusion coefficient is proportional to $N^{-1}$ and the longest internal relaxation time to $N^2$. A tagged segment has an intermediate-time mean-square displacement proportional to $t^{1/2}$ before ordinary whole-chain diffusion dominates. Entanglement adds constraints beyond this model.

A dilute-solution bead-spring model including solvent-mediated hydrodynamic interactions. In its scaling regime, a chain of size $R$ has translational diffusion coefficient of order $k_{B}T/({\eta }_{s}R)$ and longest relaxation time of order ${\eta }_s{R}^3/(k_{B}T)$. Intermediate-time segment mean-square displacements scale as $t^{2/3}$. Screening of hydrodynamic interactions in a concentrated solution changes the regime toward Rouse model behaviour; constraints from polymer entanglement require additional physics.

The effective volume governing a dissolved macromolecule’s hydrodynamic behavior and pore accessibility.

A polymer conformation model assigning allowed torsional states and statistical weights to successive backbone bonds. Correlations between torsional states can represent local stiffness beyond the fixed-angle, uniformly rotating freely rotating chain.

An interface changes polymer conformations through segment-surface affinity, solvent selectivity and confinement. Adsorbed chains make bound trains, intervening loops and free tails; end-grafted chains cross from isolated mushrooms to overlapping brushes as coverage rises. Surface binding energy competes with chain conformational entropy and crowding.

The change of an isolated flexible polymer from an expanded coil toward a dense polymer globule as its solvent becomes less favorable. In the Flory approximation, $F/(k_{B}T)\sim R^2/(N{a}^2)+v{N}^2/R^3+u{N}^3/R^6$, where the positive three-segment coefficient $u$ prevents collapse to zero size. Positive $v$ gives swollen-coil scaling, $v=0$ gives the theta temperature condition, and negative $v$ favors a dense state with $R^3\sim uN/|v|$. Finite chain length rounds the change; polymer aggregation is a distinct multi-chain process and must be controlled in an experiment.

A permanently cross-linked polymeric material that does not undergo reversible melt flow like an uncrosslinked thermoplastic.

A smallest constitutional unit whose repetition specifies a regular polymer chain.