Heterosis

hybrid vigorhybrid vigourhybrid cornheteroticcrosshybridizationvigourcross fertilisationdouble-cross hybridgenetic heterosis
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring.wikipedia
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Hybrid (biology)

hybridhybridshybridization
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring.
Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigour, often growing larger or taller than either parent.

Inbreeding depression

inbreedingdepress plant vigor
Heterosis is often discussed as the opposite of inbreeding depression although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts.
Here, even the dominant alleles result in reduced fitness if present homozygously (see also hybrid vigour).

Crossbreed

cross-breedingcrossbredcrossbreeding
The term heterosis often causes confusion and even controversy, particularly in selective breeding of domestic animals, because it is sometimes (incorrectly) claimed that all crossbred plants and animals are "genetically superior" to their parents, due to heterosis.
Crossbreeding, sometimes called "designer crossbreeding", is the process of breeding such an organism, often with the intention to create offspring that share the traits of both parent lineages, or producing an organism with hybrid vigor.

Heterozygote advantage

heterozygous advantageevolutionary trade-offadvantage in certain environments
Overdominance hypothesis. Certain combinations of alleles that can be obtained by crossing two inbred strains are advantageous in the heterozygote. The overdominance hypothesis attributes the heterozygote advantage to the survival of many alleles that are recessive and harmful in homozygotes. It attributes the poor performance of inbred strains to a high percentage of these harmful recessives. The overdominance hypothesis was developed independently by Edward M. East (1908) and George Shull (1908). Genetic variation at an overdominant locus is expected to be maintained by balancing selection. The high fitness of heterozygous genotypes favours the persistence of an allelic polymorphism in the population.
Heterozygote advantage is a major underlying mechanism for heterosis, or "hybrid vigor", which is the improved or increased function of any biological quality in a hybrid offspring.

Mule

mule trainmule trainsmules
An example of the ambiguous value judgements imposed on hybrids and hybrid vigor is the mule.
The mule is an example of hybrid vigor.

Evolution of sexual reproduction

evolution of sexsexual reproductiondeterministic mutation hypothesis
This benefit has been proposed to be a major factor in the maintenance of sexual reproduction among eukaryotes, as summarized in the article Evolution of sexual reproduction.
Recombination supplies two fault-tolerance mechanisms at the molecular level: recombinational DNA repair (promoted during meiosis because homologous chromosomes pair at that time) and complementation (also known as heterosis, hybrid vigor or masking of mutations).

George Harrison Shull

G.H. ShullGeorge H. ShullGeorge Shull
Overdominance hypothesis. Certain combinations of alleles that can be obtained by crossing two inbred strains are advantageous in the heterozygote. The overdominance hypothesis attributes the heterozygote advantage to the survival of many alleles that are recessive and harmful in homozygotes. It attributes the poor performance of inbred strains to a high percentage of these harmful recessives. The overdominance hypothesis was developed independently by Edward M. East (1908) and George Shull (1908). Genetic variation at an overdominant locus is expected to be maintained by balancing selection. The high fitness of heterozygous genotypes favours the persistence of an allelic polymorphism in the population. In proposing the term heterosis to replace the older term heterozygosis, G.H. Shull aimed to avoid limiting the term to the effects that can be explained by heterozygosity in Mendelian inheritance. Corn heterosis was famously demonstrated in the early 20th century by George H. Shull and Edward M. East after hybrid corn was invented by Dr. William James Beal of Michigan State University based on work begun in 1879 at the urging of Charles Darwin.
He also described heterosis in maize in 1908 (the term heterosis was coined by Shull in 1914) and made a number of other key discoveries in the emerging field of genetics.

Outbreeding depression

A major drawback of sexual recombination is the separation of complexes of alleles that have adapted togetherless viableoutcrossing
This is a form of outbreeding depression.
Hybrid vigor in the first generation can, in some circumstances, be strong enough to mask the effects of outbreeding depression.

Outcrossing

outcrossoutbreedingcross-fertilization
In such instances, outcrossing should result in heterosis.
Heterosis

William James Beal

BealJames BealWilliam James Beal Germination Experiment
Corn heterosis was famously demonstrated in the early 20th century by George H. Shull and Edward M. East after hybrid corn was invented by Dr. William James Beal of Michigan State University based on work begun in 1879 at the urging of Charles Darwin.
He was a pioneer in the development of hybrid corn and the founder of the W. J. Beal Botanical Garden.

Complementation (genetics)

complementationgenetic complementationcomplementation test
The genetic dominance hypothesis attributes the superiority of hybrids to the masking of expression of undesirable (deleterious) recessive alleles from one parent by dominant (usually wild-type) alleles from the other (see Complementation (genetics)).
Heterosis is the tendency for hybrid individuals to exceed their pure bred parents in size and vigor.

Zygosity

homozygousheterozygousheterozygote
Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity.
Heterosis

Charles Darwin

DarwinDarwinianCharles
Corn heterosis was famously demonstrated in the early 20th century by George H. Shull and Edward M. East after hybrid corn was invented by Dr. William James Beal of Michigan State University based on work begun in 1879 at the urging of Charles Darwin.
Enquiries about insect pollination led in 1861 to novel studies of wild orchids, showing adaptation of their flowers to attract specific moths to each species and ensure cross fertilisation.

F1 hybrid

F1F 1 hybridF2
F1 hybrid
The divergence between the (two) parent lines promotes improved growth and yield characteristics in offspring through the phenomenon of heterosis ("hybrid vigour" or "combining ability").

Detasseling

detasseled
The process of creating these hybrids often involves detasseling.
In 1908, George Harrison Shull described heterosis, also known as hybrid vigor.

Black Baldy

In cattle, crosses between Black Angus and Hereford produce a cross known as a "Black Baldy".
In addition to general hybrid vigor expected with a crossbred, the cross also produces black skin, which in sunny climates reduces the prevalence of sunburn on bare skin, such as the udder of the cow.

Flynn effect

“Flynn” effect
Michael Mingroni has proposed heterosis, in the form of hybrid vigor associated with historical reductions of the levels of inbreeding, as an explanation of the Flynn effect, the steady rise in IQ test scores around the world during the twentieth century.
Heterosis, or hybrid vigor associated with historical reductions of the levels of inbreeding, has been proposed by Michael Mingroni as an alternative explanation of the Flynn effect.

Phenotypic trait

traittraitscharacters
Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity. An offspring is heterotic if its traits are enhanced as a result of mixing the genetic contributions of its parents.

Mendelian inheritance

MendelianMendelian geneticslaws of inheritance
These effects can be due to Mendelian or non-Mendelian inheritance.

Non-Mendelian inheritance

maternal inheritancenon-Mendelianmaternal
These effects can be due to Mendelian or non-Mendelian inheritance.

Genetic variation

variationinterindividual variabilitygenetic variations
Heterosis is often discussed as the opposite of inbreeding depression although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts.

Genetic drift

driftrandom genetic driftrandom drift
Heterosis is often discussed as the opposite of inbreeding depression although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts.

Fitness (biology)

fitnessbiological fitnessreproductive fitness
Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity.

Scientific controversy

scientific controversiesscientific debatecontroversy
Dominance versus overdominance is a scientific controversy in the field of genetics that has persisted for more than a century.

Genetics

geneticgeneticistgenetically
Dominance versus overdominance is a scientific controversy in the field of genetics that has persisted for more than a century.