Heterosis

Heterosis effect referred to in genetics, plant breeding and animal breeding, the particularly strong performance of hybrids ( crossbreeds ). A heterosis effect is always present when the observed power of the first branch - generation (F1 ) is higher than the average power of this property in the parental generation. An authenticated as heterosis performance boost of mongrels is especially visible when they - are compared to their homozygous parents - if any. Thus, the heterosis effect, for example, in cereal species such as maize or rye even result in income compared to those parents (inbred lines ) to double ( and more ). Here, however, the previous inbreeding depression at higher inbreeding generations (...., I6 ) are to be considered the parents. From the perspective of orchards with vigorous growth hybrids can be seen in the short stature of their inbred lines inbreeding depression; from the perspective of these inbred lines according heterosis ( hybrid vigor, Bastardwüchsigkeit ) of the hybrids ( hybrids ). The proportion of hybrid varieties has risen sharply in recent decades. Besides the high performance comes (especially vegetables) the uniformity of hybrid varieties high importance: A plant is like the other (if the hybrids of two pure lines as parents comes ). So in 1995 when broccoli, tomatoes and Brussels sprouts represented 80 percent of the varieties of hybrid varieties.

These heterotic hybrids are heterozygous and homogeneous, corresponding to the first Mendelian rule ( Uniformitätsregel ). Then the individuals are in the F1 generation of two homozygous parents, which in turn carry different alleles of a gene in the same genotype. This is due to the fact that the double set of chromosomes each allele from the mother and one from the father.

P:                 A-B- C -D-E -F A-B- C -D-E -F                 A-B- C -D-E -F X A-B- C -D-E -F F1:                 A-B- C -D-E -F A-B- C -D-E -F                 A-B- C -D-E -F A-B- C -D-E -F While in the P generation so all chromosomal loci ( loci ) are occupied homozygous (AA or aa), they are occupied in the F1 generation all heterozygous (Aa, Bb and so on ).

Experience teaches us that are more dominant in characteristics such as productivity, vigor and like the favorable alleles. If now distinguish the homozygous parents for the complementary distribution of homozygous dominant and recessive alleles, then the feature in the hybrid will be more favorable pronounced than in each parent. It is not that purebred ( homozygous ) parents must carry less " good " dominant alleles than their hybrids. It's just that they their allelic genes in double dose ( just homozygous homozygous ) wear what " waste " is because of the dominant manifestation of the "good" allele in the phenotype - while the hybrids carrying the dominant alleles only heterozygous; but it does have a dominant allele at the relevant genes of the one and the other parent, that covers more genes from (actually more loci ).

Benefit

By genetically different possible pure-bred breeding lines of the parental generation ( parental generation = ) is reached at the crossroads that many alleles of the crossing parents are different. Stark heterozygous beings have more different genetic than purebred. They are often resistant to disease and can be better set up to changing environmental conditions. Adverse recessive related properties are also realized in the phenotype of the hybrid is not (or hardly ).

Hybrid breeding is mainly to increase fertility characteristics applied, which usually have a low heritability, that is poorly heritable are (fertility in pigs, seed yield in crop plants ).

Is used, the hybrid breeding eg bees, pigs, chickens and in crop (cereals, maize).

According to the second rule, the Mendelian heterozygosity increases but after the second filial generation (F2) from: each self-fertilization of hybrids decreases the degree of heterozygosity (and thus typically the expression of the characteristics of heterosis ) to half. Milder inbreeding, such as continued sibling mating in animals, the degree of heterozygosity decreases less strongly, but after many generations also to zero. If propagate the offspring of hybrids as usual in animals by cross-pollination, then they reach a more normal state on this inbred hybrid scale and are then neither inbred nor hybrid. If, however, the offspring of hybrids, as in many plants (eg barley) common to reproduce by self-fertilization, then they lose the generations, the heterozygosity, they are homozygous. You lose everything that was present in the output hybrid to hybrid vigor. The heterosis effect is, however, in such Plants from the outset rather small, they lose this generation sequence so little.

Note: If the two parents themselves hybrids, then they realize themselves heterosis and must be made of heterotic reasons no less productive than their intersection descendant.

In the maize breeding also three-way hybrids (Find inbred line 1 x inbred line 2) x inbred line 3 application.

Heterosis in humans?

Intelligence researchers like Michael Mingroni pull heterosis as a cause of the steady increase in human intelligence, the so-called Flynn effect into consideration.