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Penetrance is the probability of an expressed phenotype conditional on a specified genotype. It can depend on age, sex and environment. A fully penetrant recessive model assigns disease probability one to the recessive homozygote and zero to other genotypes; incomplete penetrance or phenocopies replace these indicators by intermediate probabilities.

The relationship between the phenotype of a heterozygote and those of the two corresponding homozygotes at a genetic locus. Under complete dominance, one allele gives the same phenotype in the heterozygote as in its homozygote; the term describes expression rather than the frequency or evolutionary advantage of the allele.

Two sinusoidal signals are in phase quadrature when their phase difference is a quarter cycle, for example $\cos \varphi$ and $\sin \varphi$. Their time averages have zero correlation over a cycle. In a plane wave, this separates fields such as displacement and its time derivative, velocity.

A phase difference compares two wave phases at the same position and time. For $u_1=A_1\cos (\omega t+{\varphi }_1)$ and $u_2=A_2\cos (\omega t+{\varphi }_2)$, set $\Delta \varphi ={\varphi }_2-{\varphi }_1$, modulo $2\pi$. Adding the two complex amplitudes gives the squared resultant amplitudeEqual amplitudes reinforce at $\Delta \varphi =0$ and cancel at $\Delta \varphi =\pi$; at phase quadrature the cross term vanishes in the cycle average.

For propagation through a uniform nondispersive path difference $\Delta L$, the magnitude of the accumulated phase difference is $2\pi \Delta L/\lambda$, with its sign fixed by the comparison convention. A two-path interference measurement therefore converts a small path change into an observable change of wave intensity. A stable fringe pattern requires that the relative wave phase remain sufficiently stable during the measurement.

Online text: periodic-table.rsc.org/element/17/chlorine

Cited passages: Atomic data: first ionisation energy 1251.186 kJ/mol, electron affinity 348.575 kJ/mol; Chlorine, Atomic data: electronegativity (Pauling scale) 3.16.

Online text: periodic-table.rsc.org/element/1/hydrogen

Cited passages: Atomic data: first ionisation energy 1312.05 kJ/mol, electron affinity 72.769 kJ/mol; Hydrogen, Atomic data: electronegativity (Pauling scale) 2.20.

A founder is an individual whose parents are outside the recorded pedigree. The standard pedigree likelihood assigns unrelated founders independent genotype distributions based on biological population allele or haplotype frequencies. If founders are related, their joint prior must instead account for that relationship.

For latent genotypes $G_i$ and observed phenotypes $X_i$, assume conditional phenotype independence, independent founder genotypes, and conditionally independent Mendelian transmissions. The likelihood function isThis follows by the chain rule applied to the acyclic ancestry graph, then the law of total probability over all latent genotypes. Penetrance supplies the phenotype factors and genetic recombination supplies multilocus transmission factors.

Full siblings share both parents. With unrelated, noninbred founders in a pedigree, the two parental contributions give independent opportunities for identity by descent.

// Target: biology.bigb

First cousins are children of full siblings. An otherwise outbred first-cousin pair shares two noninbred grandparents and has kinship coefficient $1/16$.

// Target: biology.bigb