Heterosis performance in industrial and yield components. Inbreeding depression and iq in a study of 72 countries. Heterosis, inbreeding depression, various theories of. Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. 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. Plant breeding is the science of changing the traits of plants in order to produce desired characteristics. However, the understanding of this biological phenomenon is limited and the genetic basis of heterosis has yet to be elucidated. To discuss the utilisation of heterosis in plant breeding it is necessary to consider its genetic basis. Abstract heterosis is of paramount agronomic impor tance and has been successfully exploited in maize hybrid breeding for decades. Genetical and physiological basis of heterosis and inbreeding 1. Heterosis refers to the phenomenon that progeny of diverse varieties of a species or crosses between species exhibit greater biomass, speed.
It is a mating system in which individuals carry alleles that originated from a common ancestor. Heterosis is due to masking of deleterious recessive alleles by dominant alleles 4. Export to pdf export to word export to pdf skip to end of banner. As with inbreeding depression, directional dominance is required for heterosis. 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. The present book attempts to fill the gap and to assess the. From 1930 to 2014 more than 3200 mutagenic plant varieties were released that have been derived. 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. New breeds are sometimes established by crossing members of two or more breeds and carefully inbreeding the original crossbred offspring. Naomi miyaji, ryo fujimoto, in advances in botanical research, 2018.
Darwin 1876 also reported that inbreeding in plants results in deterioration of vigour and the crossing in hybrid vigour. Inbreeding in humans inbreeding in animals inbreeding. Inbreeding is simply defined as the mating of relatives. Estimation of breedspecific heterosis effects for birth. The estimates of heterosis, heterobetloi ssi and inbreeding depression for pal nt hegi ht, yei dl and its components are presented in table. Gregory introduction two genetic mechanisms have been described as potential explanations for heterosis. It is quite widespread in plants which carry both male and female flowers on the same plant.
The widespread utilization of heterosis now shapes breeding programs for several agriculturally important species including maize and rice. Cross pollinated species and species reproducing asexually are highly heterozygous. Inbreeding is considered a problem in humans because inbreeding increases the chances of receiving a deleterious recessive allele inherited from a common ancestor. Pdf study of heterosis and inbreeding depression under. Edwards heterosis is the foundation of modern maize breeding programs. Thus,it might be necessary to retain gene flow among increasingly fragmented habitat patches to sustain populations that are sensitive to inbreeding. Wholegenome sequencing provides unprecedented resolution in measuring inbreeding in natural populations of conservation concern. Inbreeding is the opposite of outcrossing, which is the mating of unrelated members of the same species. Genetical and physiological basis of heterosis and inbreeding. Genotypebyenvironment interactions affecting heterosis in. Genomic insights into inbreeding depression nature.
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. Heterosis, inbreeding depression and line performance. 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. Genetical and physiological basis of heterosis and inbreeding dev hingra ph. Plants created using mutagenesis are sometimes called mutagenic plants or mutagenic seeds. Interpreting holstein association usas individual genomic prediction report when you genomic test an animal through holstein association usa, you will receive a report with a variety of traits and their genomic pta values, as well as the animals original parent average ptas.
Mammals, most other animals, and higher plants as well, have ways to minimize inbreeding. Agriculture university jobner303329, jaipur, rajasthan, india email. Now epigenetic arabidopsis hybrids show that epigenetic diversity and. Table 1 describes the range of potentially consanguineous relationships. 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. The comprehension and prediction of this phenomenon, widely used in agriculture, are a major research issue.
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. Hybrid vigor is defined by mechanisms such as dominant. Interpreting holstein association usas individual genomic. It has been used to improve the quality of nutrition in products for humans and animals. Heterosis is not only observed in adult traits like yield or plant height, but is already detected during embryo and seedling development. The contribution of epigenetic factors to inbreeding depression and heterosis remains elusive. Both heterosis and inbreeding depression are properties that are superior to either homozygote. Shull 1952 coined the term heterosis and defined it as. The hardy weinberg equilibrium was defined for the case of random mating. Estimates of heterosis and inbreeding depression for crosses of lowa maize populations abstract relative success of maize zea mays l. When these species are subjected to selfing or inbreeding they show severe reduction in vigour and fertility. Since all pure breeds of animal trace back to a relatively limited number of.
Heterosis breeding and inbreeding depression authorstream. This chapter is just barely started and does not yet have a particular case study associated with it. East superiority of an f 1 hybrid over its parents stuber 1936 states that heterozygosity at single loci confers 1994. Owing to heterosis hybrid vigor in plants, these hybrids often have superior agricultural performances in yield or disease resistance. Inbreeding simple english wikipedia, the free encyclopedia. Average heterosis it is the heterosis where f 1 is superior to mid parent value. Heterosis and inbreeding depression for each trait was worked out by utilizing the overall mean of each hybrid over replications for each trait.
Combining ability, heterosis and inbreeding depression. Outbreeding enhancementheterosis synonyms, outbreeding enhancementheterosis pronunciation, outbreeding enhancementheterosis translation, english dictionary definition of outbreeding enhancementheterosis. When the heterosis is estimated over the mid parent, i. Effects of inbreeding and heterosis in hereford lines on.
Heterosis, the phenomenon in which f 1 hybrids exhibit phenotypes superior to their parents shull 1908. Bioinformatics and computational biology program of study committee. 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. 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. Inbreeding is a term in genetics, meaning the crossing mating of closely related animals or plants.
Molecular dissection of heterosis manifestation during early maize. The genetic interpretation of inbreeding depression and. An investigation on heterosis and inbreeding depression in. Heterosis and inbreeding depression for grain yield and. Heterosis is defined as the superiority of f1 hybrid over both the parents in terms of yield andor some other characters. 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. Highyielding hybrids of cabbage can be developed successfully using heterosis breeding. Heterosis it is defined as the superiority of f 1 hybrid over both the parents in terms of yield or some other characters. 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. However in both autogamous or allogamous plants it is difficult to exclude a role of marginal overdominance which could. The superiority of the hybrids was later defined as heterosis by shull 1914. 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.
Heterosis or hybrid vigor is a phenomenon in which a hybrid progeny exhibits superior performance compared to their parental inbred lines. The natural history of inbreeding and outbreeding ed. Heterosis performance in industrial and yield components of sweet corn. The selfpollinated crops do not show inbreeding depression. It has been over 100 years since the discovery of the. We sequenced the genomes of 97 individuals to document in detail the genomic consequences of inbreeding in the population. Heterosis is directly proportional to the number of dominant genes contributed by each parent 18. Estimates of heterosis and inbreeding depression for. Heterosis and heterobeltiosis effects generally the heterosis and heterobeltiosis is associated the nonadditive effects overdominance and epistasis, although topal et al. The role of epistasis in the manifestation of heterosis.
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 concept of heterosis is widely used in plant and animal breeding. The maximum values of heterosis for gyp were obtained with the. In its opposite, outcrossing, the two parents are totally unrelated. F 1 hybrid seed production system is used for many crops and vegetables because of the high yield due to hybrid vigor. 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. Overdominant epistatic loci are the primary genetic basis.
Despite its importance in maize production, we know surprisingly little about the genetic basis of heterosis. Exploring the molecular basis of heterosis for plant breeding liu. Effects of inbreeding and heterosis in hereford lines on reproduction and maternal performance michael d. 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. 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 or hybrid vigor results in a hybrids phenotypic superiority over its founder parents for quantitative and qualitative traits. Such a genetic rescue effect might reflect the masking of fixed deleterious mutations. 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. A 632 whereas the useful heterosis values varied between 46. Superiority of dominant alleles over recessive alleles 3. Heterosis describes the phenotypic superiority of hybrids over their parents in.
Heterosis for yield contributing head traits in cabbage. There was a contribution of additive and dominance effects. 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. Heterosis from crossbreeding often appears as a sudden improvement in physical characteristics, such as size, endurance, disease resistance, etc. 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. Selffertilisation in plants is the most extreme kind of inbreeding. 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. Difference between heterosis and inbreeding depression. In genetic terminology, inbreeding is the breeding of two animals who are related to each other. Heterosis and inbreeding depression biotech articles.
Heterosis describes the superior performance of heterozygous hybrid plants over their homozygous parental inbred lines. Abstract heterosis or hybrid vigor is a natural phenomenon whereby hybrid offspring of genetically diverse individuals display improved. Since then, heterosis has been extensively exploited in plant breeding, particularly in maize. Heterosis and inbreeding depression kana ram kumawat, ravi kumawat and madhu choudhary department of plant breeding and genetics, s. Outbreeding depression michaellynch department of biology, university of oregon, eugene, or 97403 usa abstract. Towards the molecular basis of heterosis brendel group, indiana.