Population genetics

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.
Drosophila melanogaster
Gene flow is the transfer of alleles from one population to another population through immigration of individuals. In this example, one of the birds from population A immigrates to population B, which has fewer of the dominant alleles, and through mating incorporates its alleles into the other population.
The Great Wall of China is an obstacle to gene flow of some terrestrial species.
Current tree of life showing vertical and horizontal gene transfers.

Subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology.

- Population genetics
The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

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Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

John H. Gillespie

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

John H. Gillespie is an evolutionary biologist interested in theoretical population genetics and molecular evolution.

Provine in 2008

William B. Provine

Provine in 2008

William Ball Provine (February 19, 1942 – September 1, 2015) was an American historian of science and of evolutionary biology and population genetics.

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

Hill–Robertson effect

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

In population genetics, the Hill–Robertson effect, or Hill–Robertson interference, is a phenomenon first identified by Bill Hill and Alan Robertson in 1966.

This diagram illustrates how sex might create novel genotypes more rapidly. Two advantageous alleles A and B occur at random. The two alleles are recombined rapidly in a sexual population (top), but in an asexual population (bottom) the two alleles often arise in separate lineages and compete with each other.

Clonal interference

This diagram illustrates how sex might create novel genotypes more rapidly. Two advantageous alleles A and B occur at random. The two alleles are recombined rapidly in a sexual population (top), but in an asexual population (bottom) the two alleles often arise in separate lineages and compete with each other.

Clonal interference is a phenomenon in evolutionary biology, related to the population genetics of organisms with significant linkage disequilibrium, especially asexually reproducing organisms.

Evolutionary progress as a tree of life. Ernst Haeckel, 1866

Orthogenesis

Obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction towards some goal due to some internal mechanism or "driving force".

Obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction towards some goal due to some internal mechanism or "driving force".

Evolutionary progress as a tree of life. Ernst Haeckel, 1866
Lamarck's two-factor theory involves 1) a complexifying force that drives animal body plans towards higher levels (orthogenesis) creating a ladder of phyla, and 2) an adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse, inheritance of acquired characteristics), creating a diversity of species and genera. Popular views of Lamarckism only consider an aspect of the adaptive force.
Theodor Eimer
The mediaeval great chain of being as a staircase, implying the possibility of progress: Ramon Lull's Ladder of Ascent and Descent of the Mind, 1305
Reviewing Darwin's Origin of Species, Karl Ernst von Baer argued for a directed force guiding evolution.
Henry Fairfield Osborn's 1934 version of orthogenesis, aristogenesis, argued that aristogenes, not mutation or natural selection, created all novelty. Osborn supposed that the horns of Titanotheres evolved into a baroque form, way beyond the adaptive optimum.
Multiple explanations have been offered since the 19th century for how evolution took place, given that many scientists initially had objections to natural selection. Many of these theories led (solid blue arrows) to some form of orthogenesis, with or without invoking divine control (dotted blue arrows) directly or indirectly. For example, evolutionists like Edward Drinker Cope believed in a combination of theistic evolution, Lamarckism, vitalism, and orthogenesis, represented by a sequence of arrows on the left of the diagram. The development of modern Darwinism is indicated by dashed orange arrows.
A satirical opinion of Ernst Haeckel's 1874 The modern theory of the descent of man, showing a linear sequence of forms leading up to 'Man'. Illustration by G. Avery for Scientific American, 11 March 1876
Ernst Mayr considered orthogenesis effectively taboo in 1948.
The frontispiece to Thomas Henry Huxley's 1863 Evidence as to Man's Place in Nature was intended to compare the skeletons of apes and humans, but unintentionally created a durable meme of supposed "monkey-to-man" progress.
Man is But a Worm by Edward Linley Sambourne, Punch's Almanack for 1882
One of many versions of the progressionist meme: Astronomy Evolution 2 artwork by Giuseppe Donatiello, 2016

"There it remained frozen, for nearly another hundred years", until mathematicians such as Fisher provided "both models and status", enabling evolutionary biologists to construct the modern synthesis of the 1930s and 1940s.

FIT can be partitioned into FST due to the Wahlund effect and FIS due to inbreeding.

F-statistics

FIT can be partitioned into FST due to the Wahlund effect and FIS due to inbreeding.

In population genetics, F-statistics (also known as fixation indices) describe the statistically expected level of heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when compared to Hardy–Weinberg expectation.

A graphical representation of the typical human karyotype.

Fixation index

Measure of population differentiation due to genetic structure.

Measure of population differentiation due to genetic structure.

A graphical representation of the typical human karyotype.

Developed as a special case of Wright's F-statistics, it is one of the most commonly used statistics in population genetics.

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

Allele frequency spectrum

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

In population genetics, the allele frequency spectrum, sometimes called the site frequency spectrum, is the distribution of the allele frequencies of a given set of loci (often SNPs) in a population or sample.

Example scientific modelling. A schematic of chemical and transport processes related to atmospheric composition.

Coalescent theory

Model of how alleles sampled from a population may have originated from a common ancestor.

Model of how alleles sampled from a population may have originated from a common ancestor.

Example scientific modelling. A schematic of chemical and transport processes related to atmospheric composition.

The mathematical theory of the coalescent was developed independently by several groups in the early 1980s as a natural extension of classical population genetics theory and models, but can be primarily attributed to John Kingman.

Wind dispersal of dandelion seeds.

Biological dispersal

Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dispersal').

Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dispersal').

Wind dispersal of dandelion seeds.
Dispersal from parent population
Epilobium hirsutum - Seed head
Burs are an example of a seed dispersion mechanism which uses a biotic vector, in this case animals with fur.

Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution.