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.
Wright in 1954
Drosophila melanogaster
Visualization of a fitness landscape. The X and Y axes represent continuous phenotypic traits, and the height at each point represents the corresponding organism's fitness. The arrows represent various mutational paths that the population could follow while evolving on the fitness landscape.
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.

He was a founder of population genetics alongside Ronald Fisher and J. B. S. Haldane, which was a major step in the development of the modern synthesis combining genetics with evolution.

- Sewall Wright

Its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics.

- 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.

6 related topics

Alpha

Recently reported estimates of the human genome-wide mutation rate. The human germline mutation rate is approximately 0.5×10−9 per basepair per year.

Effective population size

Number of individuals that an idealised population would need to have in order for some specified quantity of interest to be the same as in the real population.

Number of individuals that an idealised population would need to have in order for some specified quantity of interest to be the same as in the real population.

Recently reported estimates of the human genome-wide mutation rate. The human germline mutation rate is approximately 0.5×10−9 per basepair per year.

The concept of effective population size was introduced in the field of population genetics in 1931 by the American geneticist Sewall Wright.

In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. fixation in the blue "allele" occurs within five generations.

Genetic drift

Change in the frequency of an existing gene variant (allele) in a population due to random chance.

Change in the frequency of an existing gene variant (allele) in a population due to random chance.

In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. fixation in the blue "allele" occurs within five generations.
Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0.5 measured over the course of 50 generations, repeated in three reproductively synchronous populations of different sizes. In these simulations, alleles drift to loss or fixation (frequency of 0.0 or 1.0) only in the smallest population.
Changes in a population's allele frequency following a population bottleneck: the rapid and radical decline in population size has reduced the population's genetic variation.
When very few members of a population migrate to form a separate new population, the founder effect occurs. For a period after the foundation, the small population experiences intensive drift. In the figure this results in fixation of the red allele.

The Wright–Fisher model (named after Sewall Wright and Ronald Fisher) assumes that generations do not overlap (for example, annual plants have exactly one generation per year) and that each copy of the gene found in the new generation is drawn independently at random from all copies of the gene in the old generation.

The corrected mathematical treatment and term "genetic drift" was later coined by a founder of population genetics, Sewall Wright.

Several major ideas about evolution came together in the population genetics of the early 20th century to form the modern synthesis, including genetic variation, natural selection, and particulate (Mendelian) inheritance. This ended the eclipse of Darwinism and supplanted a variety of non-Darwinian theories of evolution.

Modern synthesis (20th century)

The early 20th-century synthesis reconciling Charles Darwin's theory of evolution and Gregor Mendel's ideas on heredity in a joint mathematical framework.

The early 20th-century synthesis reconciling Charles Darwin's theory of evolution and Gregor Mendel's ideas on heredity in a joint mathematical framework.

Several major ideas about evolution came together in the population genetics of the early 20th century to form the modern synthesis, including genetic variation, natural selection, and particulate (Mendelian) inheritance. This ended the eclipse of Darwinism and supplanted a variety of non-Darwinian theories of evolution.
Darwin's pangenesis theory. Every part of the body emits tiny gemmules which migrate to the gonads and contribute to the next generation via the fertilised egg. Changes to the body during an organism's life would be inherited, as in Lamarckism.
Blending inheritance, implied by pangenesis, causes the averaging out of every characteristic, which as the engineer Fleeming Jenkin pointed out, would make evolution by natural selection impossible.
August Weismann's germ plasm theory. The hereditary material, the germplasm, is confined to the gonads and the gametes. Somatic cells (of the body) develop afresh in each generation from the germplasm.
William Bateson championed Mendelism.
Karl Pearson led the biometric school.
Sewall Wright introduced the idea of a fitness landscape with local optima.
Drosophila pseudoobscura, the fruit fly which served as Theodosius Dobzhansky's model organism
E. B. Ford studied polymorphism in the scarlet tiger moth for many years.
Julian Huxley presented a serious but popularising version of the theory in his 1942 book Evolution: The Modern Synthesis.
Ernst Mayr argued that geographic isolation was needed to provide sufficient reproductive isolation for new species to form.
George Gaylord Simpson argued against the naive view that evolution such as of the horse took place in a "straight-line". He noted that any chosen line is one path in a complex branching tree, natural selection having no imposed direction.
Speciation via polyploidy: a diploid cell may fail to separate during meiosis, producing diploid gametes which self-fertilize to produce a fertile tetraploid zygote that cannot interbreed with its parent species.
Ant societies have evolved elaborate caste structures, widely different in size and function.
Evolutionary developmental biology has formed a synthesis of evolutionary and developmental biology, discovering deep homology between the embryogenesis of such different animals as insects and vertebrates.
A 21st century tree of life showing horizontal gene transfers among prokaryotes and the saltational endosymbiosis events that created the eukaryotes, neither fitting into the 20th century's modern synthesis
Inputs to the modern synthesis, with other topics (inverted colours) such as developmental biology that were not joined with evolutionary biology until the turn of the 21st century

The 19th-century ideas of natural selection and Mendelian genetics were put together with population genetics, early in the twentieth century.

The population geneticist Sewall Wright focused on combinations of genes that interacted as complexes, and the effects of inbreeding on small relatively isolated populations, which could be subject to genetic drift.

Fisher in 1913

Ronald Fisher

British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic.

British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic.

Fisher in 1913
As a child
Inverforth House, North End Way NW3, where Fisher lived from 1896 to 1904
On graduating from Cambridge University, 1912
The peacock tail in flight, the classic example of a Fisherian runaway
Rothamsted Research
Memorial plaque over his remains, lectern-side aisle of St Peter's Cathedral, Adelaide
Stained glass window (now removed) in the dining hall of Caius College, in Cambridge, commemorating Ronald Fisher and representing a Latin square, discussed by him in The Design of Experiments
As a steward at the First International Eugenics Conference, 1912

Together with J. B. S. Haldane and Sewall Wright, Fisher is known as one of the three principal founders of population genetics.

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.

The concept of F-statistics was developed during the 1920s by the American geneticist Sewall Wright, who was interested in inbreeding in cattle.

The seven biggest breeders

Animal breeding

Branch of animal science that addresses the evaluation of the genetic value (estimated breeding value, EBV) of livestock.

Branch of animal science that addresses the evaluation of the genetic value (estimated breeding value, EBV) of livestock.

The seven biggest breeders

The scientific theory of animal breeding incorporates population genetics, quantitative genetics, statistics, and recently molecular genetics and is based on the pioneering work of Sewall Wright, Jay Lush, and Charles Henderson.