Genetic Analysis of Heterosis

Hybrid vigor is the increased function of a genetically superior offspring from its parents which normally resulted in increased size, viability, growth rate and productivity in next F1 generation. Charles Darwin for the first time in 1876 described heterosis, which was rediscovered by shull and east in 1908.Shull (1952) defined the heterosis as “the interpretation of increased vigor, size, fruitfulness, speed of development, resistance to disease and to insect pests, or to climatic rigors of any kind, manifested by crossbred organisms as compared with corresponding inbreds, as the specific results of unlikeness in the constitutions of the uniting parental gametes.”.It has also been reported to exhibit the expression of adaptive traits of increased fertility and biotic and abiotic stress resistance respectively. (Dobzhansky, 1950).
Genetic models to explain heterosis
Traditional genetic analyses of heterosis are based on the quantitative effects of the genes between two opposite inbred lines.
Three major classical genetic models have been suggested to explain the hybrid vigor: the dominance hypothesis explains increased vigor to the action at multiple loci of favorable dominant alleles from both parents, cancelling of deleterious recessives alleles contributed by one parent by dominant alleles contributed by the other parent (Bruce 1910; Jones 1917; Xiao et al. 1995; Cockerham and Zeng 1996, Davenport 1908, Keeble and Pellew (1910) and Jonbes in 1917), overdominance indicated the existence of loci at which the heterozygous state is superior to either homozygotes.Shull 1908; East 1936; Crow 1948; Stuber et al. 1992 (Crow 1948; Hull 1945), and epistasis (Powers 1944; Williams 1959). pseudo-overdominance refers to a particular situation, in which tightly linked genes with favorable dominant alleles in repulsion phase in the parental lines result in an apparent overdominance when combined in the hybrid. Finally, the interaction of favorable alleles from the

References: Auger D L, Gray A D, Ream T S, et al. Nonadditive gene expression in diploid and triploid hybrids of maize. Genetics, 2005, 169: 389―397. Barbosa-Neto J F, Sorrells M E, Cisar G. Prediction of heterosis in wheat using coefficient of parentage and RFLP-based estimates of genetic relationship. Genome, 1996, 39: 1142―1149. Betrán F J, Ribaut J M, Beck D, et al. Genetic diversity, specific combining ability, and heterosis in tropical maize under stress and nonstress environments. Crop Sci, 2003, 43: 797―806. Birchler J A, Auger D L, Riddle N C. In search of the molecular basis of heterosis. Plant Cell, 2003, 15: 2236―2239. Boppenmaier J, Melchinger A E, Seitz G, et al. Genetic diversity for RFLPs in European maize inbreds. III: Relation to performance of crosses within versus between heterotic groups for grain traits. Pl Breed, 1993, 111: 217―226 Bruce A B Burstin J, Charcosset A, Barriere Y, et al. Molecular markers and protein quantities as genetic descriptors in maize. II: Prediction of performance of hybrids for forage traits. Pl Breed, 1995, 114: 427―433 Davenport C B Dudley J W, Saghai Maroof M A, Rufener G K. Molecular markers and grouping of parents in maize breeding programs. Crop Sci, 1991, 31: 718―723. East E M. Inbreeding in corn. Rep Conn Agric Exp Stn, 1908, 419―428. Frei O M, Stuber C W, Goodman M M. Use of allozymes as genetic markers for predicting performance in maize single cross hybrids. Crop Sci, 1986, 26: 37―42. Godshalk E B, Lee M, Lankey K R. Relationship of restriction fragment length polymorphism to single-cross hybrid performance of maize. Theor Appl Genet, 1990, 80: 273―280. Guo M, Rupe M A, Yang X, et al. Genome-wide transcript analysis of maize hybrids: allelic additive gene expression and yield heterosis. Theor Appl Genet, 2006, 113(5): 831―845. Hallauer A R and Miranda J B. Quantitative genetics in maize breeding. 2nd ed. Oxford: Iowa State University Press, 1988. Huang Y, Zhang L, Zhang J, et al. Heterosis and polymorphisms of gene expression in an elite rice hybrid as revealed by microarray analysis of 9198 unique ESTs. Plant Mol Biol, 2006, 62: 579―591. Keeble F, Pellew C. The mode of inheritance of stature and of time of flowering in peas (Pisum sativum). J Genet, 1910, 1: 47―56 Knight R Lee M, Godshalk E B, Lamkey K R, et al. Association of restriction fragment length polymorphism among maize inbreds with agronomic performance of their crosses. Crop Sci, 1989, 29: 1067―1071. M.S.S. Abdel-Hady (2006) “ Heterosis and Combining Ability Effects for Callus Growth of Wheat (Triticum durum, Desf.) In Vitro. , Journal of Applied Sciences Resaerch 2(6): 360-363. Melchinger A E, Boppenmaier J, Dhillon B S, et al. Genetic diversity for RFLPs in European maize inbreds: II. Relation to performance of hybrids within versus between heterotic groups for forage traits. Theor Appl Genet, 1992, 84: 672―681. Melchinger A E, Lee M, Lamkey K R, et al. Genetic diversity for restriction length polymorphisms: Relation to estimated genetic effects in maize inbreds. Crop Sci, 1990, 31: 1033―1040. Melchinger A E. Genetic diversity and heterosis. In: Coors J G, Pandey S, eds. The Genetics and Exploitation of Heterosis in Crops. Madison, Wisconsin: Am Soc Agronomy and Crop Sci Soc Am, 1999. 99―118. Meyer R C, Törjék O, Becher M, et al. Heterosis of biomass production in Arabidopsis. Establishment during early development. Plant Physiol, 2004, 134: 1813―1823. Hans-Peter Piepho Optimal Allocation in Designs for Assessing Heterosis From cDNA Gene Expression Data Genetics 171: 359–364 (September 2005) Meyer S, Pospisil H, Scholten S Osborn T C, Pires J C, Birchler J A, et al. Understanding mechanisms of novelgene expression in polyploids. Trends Genet, 2003, 19: 141―147. Shieh G J, Thseng F S. Genetic diversity of Tainan-white maize inbred lines and prediction of single cross hybrid performances using RAPD markers. Euphytica, 2002, 124: 307―313. Shull G H. Duplicated genes for capsule from in Bursa bursapastoris. Z Indukt Abstammungs u Vererbungsl, 1914, 12: 97―149. Shull, G. H., 1908 The composition of a field of maize. Ann. Breed. Assoc. Rep. 4: 296–301. Smith O S, Smith J S C, Bowen S L, et al. Similarities among a group of elite maize inbreds as measured by pedigree, F1 grain yield, grain yield, heterosis and RFLPs. Theor Appl Genet, 1990, 80: 833―840 Smith O S, Smith J S C, Bowen S L, et al Song R, Messing J. Gene expression of a gene family in maize based on noncollinear haplotypes. Proc Natl Acad Sci USA, 2003, 100: 9055―9060. Springer N M, Stupar R M. Allelic variation and heterosis in maize: How do two halves make more than a whole? Cold Spring Harbor: Cold Spring Harbor Laboratory Press, 2007. Stokes D, Morgan C, O’Neill C, et al. Evaluating the utility of Arabidopsis thaliana as a model for understanding heterosis in hybrid crops. Euphytica, 2007, 156: 157―171. Stokes D, Morgan C, O’Neill C, et al. Transcriptome-based predictive modelling of heterosis. Abstract Int. Symposium Heterosis in Plants, 18-20 May, 2006, Potsdam-Golm. Stupar R M, Gardiner J M, Oldre A G, et al. Gene expression analyses in maize inbreds and hybrids with varying levels of heterosis. Plant Biol, 2008, 8: 33. Sun Q X, Ni Z F, Liu Z Y. Differential gene expression between wheat hybrids and their parental inbreds in seedling leaves. Euphytica, 1999, 106: 117―123. Swanson-Wagner R A, Jia Y, DeCook R, et al. All possible modes of gene action are observed in a global comparison of gene expression in a maize F1 hybrid and its inbred parents. Proc Natl Acad Sci USA, 2006, 103: 6805―6810. Vuylsteke M, Kuiper M, Stam P. Chromosomal regions involved in hybrid performance and heterosis: their AFLP-based identification and practical use in prediction models. Heredity, 2000, 85: 208― 218. Xie Z, Wang J, Cao M, et al. Pedigree analysis of an elite rice hybrid using proteomic approach. Proteomics, 2006, 6: 474―486. Yao Y, Ni Z, Zhang Y, et al. Identification of differential expressed genes in leaf and root between wheat hybrid and ist parental inbreds using PCR-based cDNA subtraction. Plant Mol Biol, 2005, 58: 367―384. Zanoni U, Dudley J W. Comparison of different methods of identifying inbreds useful for improving elite maize hybrids. Crop Sci, 1989, 29: 577―582. Disease Resistance in Hybrids Resistance genes could be accumulated in the hybrids (Stroike 1987)