Heterosis is a term used in genetics and selective breeding. Genetics (from Ancient Greek grc-Latn genetikos, “genitive” and that from grc-Latn genesis, “origin” a discipline of Biology, is This article focuses on selective breeding in domesticated animals The term heterosis, also known as hybrid vigor or outbreeding enhancement, describes the increased strength of different characteristics in hybrids; the possibility to obtain a genetically superior individual by combining the virtues of its parents. In Biology, hybrid has two meanings The first meaning is the result of interbreeding between two animals or plants of different taxa.

A mixed-breed dog

Heterosis is the opposite of inbreeding depression, which occurs with increasing homozygosity. A dog hybrid (also called a designer dog is a new term for an individual Dog with with ancestry in two different purebred Dog breeds traditionally Inbreeding depression is reduced fitness in a given Population as a result of breeding of related individuals Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous The term often causes controversy, particularly in terms of the selective breeding of domestic animals, because it is sometimes believed that all crossbred plants or animals are genetically superior to their parents; this is not necessarily true. This is a list of animals that have been domesticated by Humans. A crossbreed or crossbred usually refers to an animal with Purebred parents of two different breeds varieties or populations When a hybrid is seen to be superior to its parents, this is known as hybrid vigor. When the opposite happens, and a hybrid inherits traits from their parents that makes them unfit for survival, the result is referred to as outbreeding depression. In Evolutionary biology, outbreeding depression refers to cases when Offspring from crosses between individuals from different populations have lower fitness than Typical examples of this are crosses between wild and hatchery fish that have incompatible adaptations.

Genetic basis of heterosis

Genetic basis of heterosis. Deleterious recessive genes avoidance hypothesis. Scenario A. Fewer genes are under-expressed in the homozygous individual. As well, gene expression in the offspring is equal to the expression of the best parent. Overdominance hypothesis. Scenario B. Over-expression of certain genes in the homozygous. (The size of the circle depicts the expression level of gene A)

Two leading hypotheses explain the genetic basis for fitness advantage in heterosis. Fitness (often denoted w in Population genetics models is a central concept in evolutionary theory.

The overdominance hypothesis implies that the combination of divergent alleles at a particular locus will result in a higher fitness in the heterozygote than in the homozygote. Overdominance is a condition in genetics where the Phenotype of the heterozygote lies outside of the phenotypical range of both homozygote parents An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous Take the example of parasite resistance controlled by gene A, with two alleles A and a. The heterozygous individual will then be able to express a broader array of parasite resistance alleles and thus resist a broader array of parasites. The homozygous individual, on the other hand, will only express one allele of gene A (either A or a) and therefore will not resist as many parasites as the heterozygote.

The second hypothesis involves avoidance of deleterious recessive genes (also called the general dominance hypothesis), such that heterozygous individuals will express fewer deleterious recessive alleles than its homozygous counterpart.

The two hypotheses will have different consequences on the gene expression profile of the individuals. Gene expression is the process by which inheritable information from a Gene, such as the DNA sequence, is made into a functional Gene product, such If over-dominance is the main cause for the fitness advantages of heterosis, then there should be an over-expression of certain genes in the heterozygous offspring compared to the homozygous parents. On the other hand, if avoidance of deleterious recessive genes is the cause, then there should be fewer genes that are under-expressed in the heterozygous offspring compared to the parents. Furthermore, for any given gene, the expression should be comparable to the one observed in the best of the two parents.

Hybrid corn

Nearly all the field corn now grown in the United States and most other developed nations is hybrid corn. Modern corn hybrids substantially outyield conventional cultivars and respond better to fertilization.

Heterosis in maize was famously demonstrated in the early 20th century by George H. Maize (ˈmeɪz ( Zea mays L. ssp mays) known as corn in some countries is a cereal grain domesticated in Mesoamerica 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. Michigan State University ( MSU) is a co-educational public Research university in East Lansing, Michigan USA. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life Dr. Beal's work led to the first published account of a field experiment demonstrating hybrid vigor in corn, by Eugene Davenport and Perry Holden, 1881. These various pioneers of botany and related fields showed that crosses of inbred lines made from a Southern dent and a Northern flint, respectively, showed substantial heterosis and outyielded conventional cultivars of that era. However, at that time such hybrids could not be economically made on a large scale for use by farmers. Donald F. Jones at the Connecticut Agricultural Experiment Station, New Haven invented the first practical method of producing a high-yielding hybrid maize in 1914-1917. Donald Forsha Jones was a United States Maize geneticist and practical Corn breeder at the Connecticut Agricultural Experiment Station, New Haven Connecticut ( is a state located in the New England region of the northeastern United States of America. An agricultural experiment station is a research center that conducts scientific investigations to solve problems and suggest improvements in the food and Agriculture industry Jones' method produced a double-cross hybrid, which requires two crossing steps working from four distinct original inbred lines. Later work by corn breeders produced inbred lines with sufficient vigor for practical production of a commercial hybrid in a single step, the single-cross hybrids. Single-cross hybrids are made from just two original parent inbreds. They are generally more vigorous and also more uniform than the earlier double-cross hybrids. The process of creating these hybrids often involves detasseling. Detasseling is the act of removing the Pollen -producing tassel from a corn (maize plant and placing it on the ground

Hybrid livestock

The concept of heterosis is also applied in the production of commercial livestock. Livestock is the term used to refer (singularly or plurally to a Domesticated Animal intentionally reared in an agricultural setting to produce such as Food In cattle, hybrids between Black Angus and Hereford produce a hybrid known as a “Black Baldy. Angus cattle is a term that refers in much of the world (though not in the United States) to either or both (collectively of two types of naturally hornless Cattle Hereford Cattle are a widely used breed in Temperate areas mainly for beef production Black Baldy is a term used in Australia, New Zealand and North America for a type of beef cattle produced by crossing Hereford cattle with a ” In swine, “blue butts” are produced by the cross of Hampshire and Yorkshire. Pigs, also called hogs or' swine', are Ungulates which have been domesticated as sources of food leather and similar products since ancient times The Hampshire pig is a domestic swine breed identified by its black body with a whitish belt around its middle covering its front legs Other more exotic hybrids such as “beefalo” are also used for specialty markets. Beefalo are a fertile hybrid offspring of domestic Cattle, Bos taurus, and the American Bison, Bison bison (generally called

Within poultry, sex-linked genes have been used to create hybrids in which males and females can be sorted at one day old by color. Poultry is the category of Domesticated Birds which some humans keep for the purpose of collecting their eggs, or kill for their Meat and/or Sex linkage is the phenotypic expression of an Allele that is related to the chromosomal sex of the individual Specific genes used for this are genes for barring and wing feather growth. Crosses of this sort create what are sold as Black Sex-links, Red Sex-links, and various other crosses that are known by trade names.

Commercial broilers are produced by crossing different strains of White Rocks and White Cornish, the Cornish providing a large frame and the Rocks providing the fast rate of gain. The hybrid vigor produced allows the production of uniform birds with a marketable carcass at 6-9 weeks of age.

Likewise, hybrids between different strains of White Leghorn are used to produce laying flocks that provide the majority white eggs for sale in the United States.

See also

• F1 hybrid

References