East superiority of an f 1 hybrid over its parents stuber 1936 states that heterozygosity at single loci confers 1994. Interpreting holstein association usas individual genomic. We sequenced the genomes of 97 individuals to document in detail the genomic consequences of inbreeding in the population. Selffertilisation in plants is the most extreme kind of inbreeding. Average heterosis it is the heterosis where f 1 is superior to mid parent value. A 632 whereas the useful heterosis values varied between 46. Heterosis and heterobeltiosis effects generally the heterosis and heterobeltiosis is associated the nonadditive effects overdominance and epistasis, although topal et al.
Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to methods that make use of knowledge of. Edwards heterosis is the foundation of modern maize breeding programs. Incestuous marriages involving firstdegree relatives are generally strongly discouraged throughout the world, and in many countries, the most consanguineous legal relationship is the marriage of firstcousins bittles, 2004. This chapter is just barely started and does not yet have a particular case study associated with it. Heterosis and inbreeding depression kana ram kumawat, ravi kumawat and madhu choudhary department of plant breeding and genetics, s. Abstract heterosis or hybrid vigor is a natural phenomenon whereby hybrid offspring of genetically diverse individuals display improved. Heterosis and inbreeding depression pdf heterosis is defined as the superiority of f1 hybrid over both the parents in terms of yield andor some other characters. Bioinformatics and computational biology program of study committee. The hardy weinberg equilibrium was defined for the case of random mating. Now epigenetic arabidopsis hybrids show that epigenetic diversity and.
Heterosis and inbreeding depression for each trait was worked out by utilizing the overall mean of each hybrid over replications for each trait. The estimates of heterosis, heterobetloi ssi and inbreeding depression for pal nt hegi ht, yei dl and its components are presented in table. The contribution of epigenetic factors to inbreeding depression and heterosis remains elusive. Hybrid vigor is defined by mechanisms such as dominant. Heterosis describes the superior performance of heterozygous hybrid plants over their homozygous parental inbred lines. Heterosis describes the phenotypic superiority of hybrids over their parents in. Since then, heterosis has been extensively exploited in plant breeding, particularly in maize. Genomic insights into inbreeding depression nature. Such a genetic rescue effect might reflect the masking of fixed deleterious mutations. Up to now the phenomenon of heterosis in corn has been explained mainly by one of two alternatives. After maize hybrid was first utilized in field on a large scale in usa in 1930s, heterosis of other crops such as rice, sorghum, rape, and vegetable etc began to be widely used in production, and had made great achievements in crop breeding by the end of last century, mainly contributed to notable increasing of crop yield. Abstract heterosis is of paramount agronomic impor tance and has been successfully exploited in maize hybrid breeding for decades.
Both heterosis and inbreeding depression are properties that are superior to either homozygote. Heterosis and inbreeding depression by shreyartha mukherjee a dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of doctor of philosophy major. It is quite widespread in plants which carry both male and female flowers on the same plant. Heterosis or hybrid vigor results in a hybrids phenotypic superiority over its founder parents for quantitative and qualitative traits. In cross fertilized plants in which the phenomenon of heterosis is very important, such as maize, it appears that a great part can be explained by the mutation load.
Plants created using mutagenesis are sometimes called mutagenic plants or mutagenic seeds. Inbreeding is considered a problem in humans because inbreeding increases the chances of receiving a deleterious recessive allele inherited from a common ancestor. The comprehension and prediction of this phenomenon, widely used in agriculture, are a major research issue. Genetical and physiological basis of heterosis and inbreeding.
Heterosis, inbreeding depression and line performance. Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. The nature and magnitude of heterosis was computed as per cent increase or decrease of the mean values of f 1 over mid parent, better parent bp and standard variety sv. Mutation breeding, sometimes referred to as variation breeding, is the process of exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to be bred with other cultivars. Kotiaho,1,2 kari nissinen3 and mikael puurtinen1,4 1 department of biological and environmental science, university of jyvaskyl a, jyv askyl a, finland 2 natural history museum, university of jyvaskyl a, jyv askyl a. When these species are subjected to selfing or inbreeding they show severe reduction in vigour and fertility. Genetical and physiological basis of heterosis and inbreeding dev hingra ph. The purpose of this discussion paper is to facilitate a broad discussion with organic farmers and other stakeholders, such as breeding companies, interest groups and policymakers.
It has been over 100 years since the discovery of the. Darwin 1876 also reported that inbreeding in plants results in deterioration of vigour and the crossing in hybrid vigour. The result of this study was a new approach to the heterosis problem, which in turn led to a new breeding procedure that has already been used in the production. On the basis of his experiments beal 18771882 concluded that f 1 hybrids yield as much as 40 percent more of the parental varieties from subsequent studies on intervarietal crosses in maize, it was observed that some of the hybrids show heterosis. Inbreeding simple english wikipedia, the free encyclopedia. The phenomenon of true heterosis is distinguished from the yield increase brought about by the union of cumulative factors in that its effect is almost confined to the f1 generation, later generations falling off again in yield up to a certain minimumthe inbreeding minimum. In many species, the controlled crossing of selected parental components, mainly inbred lines, is employed to maximize heterosis and thus agronomic performance of the resulting f 1 hybrids. Heterosis and inbreeding depression for grain yield and. Outbreeding depression michaellynch department of biology, university of oregon, eugene, or 97403 usa abstract. Heterosis and inbreeding depression biotech articles. The genetic interpretation of inbreeding depression and. In genetic terminology, inbreeding is the breeding of two animals who are related to each other. Owing to heterosis hybrid vigor in plants, these hybrids often have superior agricultural performances in yield or disease resistance. Plant breeding is the science of changing the traits of plants in order to produce desired characteristics.
The key difference between heterosis and inbreeding depression is that heterosis is the enhancement of traits due to the mixing of genes from two different individuals during outbreeding while inbreeding depression is the reduced biological fitness of offspring due to the increased homozygosity as a result of inbreeding between closely related. It is a mating system in which individuals carry alleles that originated from a common ancestor. Detrimental effects associated with inbreeding are attributable to the increased homozygosity. Wholegenome sequencing provides unprecedented resolution in measuring inbreeding in natural populations of conservation concern. F 1 hybrid seed production system is used for many crops and vegetables because of the high yield due to hybrid vigor. Genotypebyenvironment interactions affecting heterosis in. Table 1 describes the range of potentially consanguineous relationships. Shull 1952 coined the term heterosis and defined it as. However in both autogamous or allogamous plants it is difficult to exclude a role of marginal overdominance which could. Expected means and variances among inbred lines and their crosses c. Genetical and physiological basis of heterosis and inbreeding 1.
Inbreeding in humans inbreeding in animals inbreeding. The harmful effect of inbreeding and the higher vigor of hybrids compared to their inbred parents were first observed by darwin 1876 and then described in maize by east 1908 and shull 1908. Since all pure breeds of animal trace back to a relatively limited number of. Heterosis, inbreeding depression, various theories of.
Heterosis is directly proportional to the number of dominant genes contributed by each parent 18. Heterosis performance in industrial and yield components. Superiority of dominant alleles over recessive alleles 3. From 1930 to 2014 more than 3200 mutagenic plant varieties were released that have been derived. When the heterosis is estimated over the mid parent, i. Naomi miyaji, ryo fujimoto, in advances in botanical research, 2018. Combining ability, heterosis and inbreeding depression. Molecular dissection of heterosis manifestation during early maize. Exploring the molecular basis of heterosis for plant breeding liu. There was a contribution of additive and dominance effects. Heterosis refers to the phenomenon that progeny of diverse varieties of a species or crosses between species exhibit greater biomass, speed.
Inbreeding is a term in genetics, meaning the crossing mating of closely related animals or plants. As with inbreeding depression, directional dominance is required for heterosis. The role of epistasis in the manifestation of heterosis. Thus,it might be necessary to retain gene flow among increasingly fragmented habitat patches to sustain populations that are sensitive to inbreeding. Export to pdf export to word export to pdf skip to end of banner. Effects of inbreeding and heterosis in hereford lines on reproduction and maternal performance michael d. Pdf study of heterosis and inbreeding depression under.
Inbreeding depression and iq in a study of 72 countries. The widespread utilization of heterosis now shapes breeding programs for several agriculturally important species including maize and rice. The mean heterosis of hybrids compared with the parents was positive for most traits. Gregory introduction two genetic mechanisms have been described as potential explanations for heterosis. However, the understanding of this biological phenomenon is limited and the genetic basis of heterosis has yet to be elucidated. Outbreeding enhancementheterosis synonyms, outbreeding enhancementheterosis pronunciation, outbreeding enhancementheterosis translation, english dictionary definition of outbreeding enhancementheterosis. It has been used to improve the quality of nutrition in products for humans and animals. In the same way the phenomenon of heterosis differs from the effect of complementary factors where there is no. Inbreeding and linebreeding what are inbreeding and linebreeding, and what effect do they have. The superiority of the hybrids was later defined as heterosis by shull 1914. The concept of heterosis is widely used in plant and animal breeding. Towards the molecular basis of heterosis brendel group, indiana. Inbreeding with close relatives and outbreeding with members of distant populations can both result in deleterious shifts in the means of fitnessrelated characters, most likely for very different reasons.
Highyielding hybrids of cabbage can be developed successfully using heterosis breeding. Heterosis breeding and inbreeding depression authorstream. Estimates of heterosis and inbreeding depression for crosses of lowa maize populations abstract relative success of maize zea mays l. Difference between heterosis and inbreeding depression. The present book attempts to fill the gap and to assess the. New breeds are sometimes established by crossing members of two or more breeds and carefully inbreeding the original crossbred offspring. To discuss the utilisation of heterosis in plant breeding it is necessary to consider its genetic basis. The selfpollinated crops do not show inbreeding depression. The natural history of inbreeding and outbreeding ed. No comprehensive and critical analysis of the phenomenon of heterosis in economic plants has been published for the last three decades since the now classical book heterosis, edited by j. Heterosis is defined as the superiority of f1 hybrid over both the parents in terms of yield andor some other characters. Average heterosis fl mpmp x 100 where, f, is the mean value of7, and mp is the mean value of two parents involved in the cross. Heterosis, the phenomenon in which f 1 hybrids exhibit phenotypes superior to their parents shull 1908.
Inbreeding is simply defined as the mating of relatives. Heterosis or hybrid vigor is a phenomenon in which a hybrid progeny exhibits superior performance compared to their parental inbred lines. For specific leaf areanegative heterosis is desirable because in groundnutuhasbeendemonstrated. Overdominant epistatic loci are the primary genetic basis. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Heterosis is due to masking of deleterious recessive alleles by dominant alleles 4. Mammals, most other animals, and higher plants as well, have ways to minimize inbreeding. The maximum values of heterosis for gyp were obtained with the. Agriculture university jobner303329, jaipur, rajasthan, india email. In its opposite, outcrossing, the two parents are totally unrelated. An investigation on heterosis and inbreeding depression in. Cross pollinated species and species reproducing asexually are highly heterozygous. Effects of inbreeding and heterosis in hereford lines on. Heterosis it is defined as the superiority of f 1 hybrid over both the parents in terms of yield or some other characters.
Following functional extinction in the 1960s, a single pair of wolves recolonized the scandinavian peninsula in the 1980s. Heterosis for yield contributing head traits in cabbage. Heterosis performance in industrial and yield components of sweet corn. Estimates of heterosis and inbreeding depression for.
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