An intriguing phenotypic consequence of polyploidy and aneuploidy is the difference in performance due to the number of genomic complements, or to variation in doses of whole chromosomes or portions of chromosomes, and these consequences may have implications for heterosis [ 12, ].
Within that are three top stud herds, and a multiplier herd. In a related study, Guo et al. Consider, for example, the possibility that a species with 10 chromosomes has a pair of loci on each of the 10 chromosomes 1 centimorgan apart in repulsion phase with dominant gene action.
Hybridization in chickpea offers many advantages as the creation of new varietal types highly productive, the modulation by the heterozygous state of unusable genes in the homozygous state and the accumulation of dominant genes to the improvement of nutritional quality in early generations of the breeding program.
View at Google Scholar N. Heterotic patterns used by plant breeders [ 73 ] provide a useful conceptual model to discuss heterosis in isolated populations. Furthermore, two inbred lines from the population exceeded the performance of the hybrid, consistent with Genetic analysis of heterosis proposition that, under the dominance hypothesis, it is possible to produce a homozygous individual that contains all the favorable alleles that produced the observed hybrid performance.
In most cases, vigor would be expected to be reduced in these mutants and by these treatments. While it is certain that future discoveries will explain more about the process of heterosis, it is my opinion that a new and undiscovered molecular mechanism is not needed to ultimately explain heterosis.
Therefore, this metabolic and signaling pathway provides ample opportunity for the expression of epistatic gene action. An early and still prevalent model of alternative allelic states is the presence of every gene in all individuals of a species with an array of sequence variants that could confer minor to Genetic analysis of heterosis functional consequences including intermediate-to-complete loss-of-function alleles.
However, many interspecific hybrids suffer from reduced longevity and reductions in fertility. It is also commensurate with allele- and locus-specific observations of paramutation [ 97 — 99 ] in which the allelic interaction results in a heritable change in expression state, an observation inconsistent with the tenets of quantitative genetic theory.
The triple testcross analysis compares the relative performance of segregating progeny when testcrossed to both parents and to the F1 hybrid. A recent study in rice provides similar support for the role of GA in heterosis for biomass accumulation [ 55 ]. Quantitative trait locus QTL mapping studies in maize are also consistent with dominance versus overdominance as the prevalent type of gene action underlying heterosis for productivity.
The scientific basis for the economic success was founded by the American geneticists and plant breeders D. Note also that the level of linkage disequilibrium in these materials was likely quite low, minimizing confounding effects of pseudooverdominance.
An accumulation of the effects of a large number of genes with small effects and some level of dominance, taken in the context of recombination across the genome, is sufficient to explain heterosis and is consistent with directed and natural evolution.
Finally, heritable epialleles [ 71 ] provide a sequence-independent mechanism to produce altered expression levels that might be able to more rapidly revert to support rapid direct or natural evolutionary change. Genomic Analysis of Heterosis Phenotype is the result of the interpretation of genetic information through the processes of transcription, translation, and metabolism and development.
Inthe company started developing a self-perpetuating composite to balance tropical adaptation, fertility and meat quality traits, while retaining hybrid vigour.
Inbreeding due to drift, population isolation, or consanguineous mating by plan or by chance reduces vigor of individuals or populations due to increasing homozygosity of deleterious alleles.
An allele of the enzyme with high activity was combined with an allele that had heat tolerance. It is notable that the hybrid is generally a predictable combination of the inbred parents and that it does not exhibit genomewide luxuriant transcription levels which are not predictable by parental expression levels as suggested by some models [ 79 ].
Non-additive gene action could result from genetic and epigenetic intra-allelic interactions including paramutation, or from interallelic interactions epistasis. Furthermore, polyploids have additional opportunity for epistatic interactions due to potential segregation of interacting loci contributed by the component genomes as well as independent segregation of allelic variants at homoeologous loci.
Various studies have measured small RNA levels in inbreds and hybrids, some of which present a strong suggestion for the role of small RNAs in heterosis [ 8081 ]. If overdominance was the primary basis of heterosis, the populations would diverge due to selection and increase homozygosity of alternative alleles within the populations to maximize heterozygosity and performance of the population cross.
The weight of vegetative matter of F2 and parents cultivar were obtained by weighing 20 dry plants without seeds; and the means obtained by SPSS procedure are included in Table 4.
Contrary to traditional practices this results in the separation of the production of seed and nutrition. All of these allele-generating mechanisms—SNPs, transposons, PAVs, and epialleles—are consistent with the hypothesis that locus-specific intra-allelic interactions with some degree of dominance are responsible for heterosis.
Investigation of the distribution of heterozygous loci, among 12 commercial cotton hybrids, revealed a potential role for these regions in heterosis. Summary and Integration It is clear that much remains to be learned about genome composition and the role of transcription, translation, and posttranslational mechanisms in interpreting genes into phenotype.
Furthermore, they report that application of a demethylating agent, 5-azacytidine, to inbreds restored productivity to the hybrid level. The relatively small amount of roughly 20 genes is enough for the whole range of colours that is displayed by the flowers of snapdragons.
These differences in performance can occur independent of any allelic diversity. Despite chickpea is autogamous this species showed big potentialities in improvement by expressing a big rate of heterosis we measured high value of gain in yield and its components in Table 1.
The harvest of the plants F2 and the parents was conducted at the end of plant physiological maturity yield and its components were counted at the stage of maturity of plants and noted on ten plants F2 and parental cultivar in random number of pods and grains F3 per plant.
Based on the fact that some traits exhibited overdominance while others did not, the authors argued that this study supported true overdominance as opposed to pseudooverdominance.
The number of pods by plant was less stable during the two growing seasons excepted for B1K2 and B1D2 have the most adapted genotypes. The search for the genes and alleles that underlie heterosis, as well as for broader allele-independent, genomewide mechanisms, has encompassed many species and systems.
Matching genetics to environment often requires composite breeding.The genetic phenomenon of heterosis, or hybrid vigor, has benefited agriculture and fascinated geneticists for over years.
Heterosis describes the situation in which hybrid offspring exhibit phenotypic performance that is superior to that of their parents Proteomic analysis of heterosis during maize seed germination. The Genetics Society of America (GSA), founded inis the professional membership organization for scientific researchers and educators in the field of genetics.
Our members work to advance knowledge in the basic mechanisms of inheritance, from the molecular to the population level. For quantitative genetic analysis, the deviation of the hybrid relative to the mid-parent is the relevant value.
In a practical context, high-parent heterosis, which measures the superiority of the hybrid relative to the best parent, is the important metric. M. Han et al., “MicroRNA transcriptomic analysis of heterosis during maize seed.
Heterosis, also known as ‘hybrid vigor’, is a well-known phenomenon whereby hybrid offspring resulting from cross pollination exhibit greater vigor than either parent.
Here, Hochholdinger and Baldauf provide an overview of this fascinating biological phenomenon and what is known about the underlying genetics and mechanisms. Official Methods of Analysis. 18th Edition, AOAC, International, Maryland, USA. Department of Biological Sciences Genetics and Molecular Biology, Faculty of sciences of Tunis,University of Tunis el Manar, Tunisia The stability of heterosis through segregating generations is possible but not evident suggesting the impact of parent.
Request PDF on ResearchGate | Genetic analysis of heterosis for maize grain yield and its components in a set of SSSL testcross populations | The present study aimed to dissect the genetic basis of heterosis for grain yield and its components in maize (Zea mays L.).Download