Species is a group of potentially interbreeding natural populations that are reproductively isolated from other groups. Reproductive barriers are important to maintain identity of established species. Reproductive isolation is divided into two forms depending on the stage in which it occurs: Prezygotic barriers and Postzygotic barriers. Prezygotic barriers act earlier in the life history preventing the formation of hybrid zygotes and consist of forces that reduce the chance of mating success. Postzygotic barriers, on the other hand, result from fitness aberration in hybrids causing hybrid sterility and thus preventing the exchange of genes between species or subspecies2.
Hybrid incompatibility (HI) is a measurable reduction in fitness in F1, F2, or BC1 generation of interspecific hybrids. According to The Dobzhansky–Muller Model, Hybrid Incompatibilities results from a deleterious interaction between functionally diverged genes from the hybridizing species. In this model, independent mutations appear and get fixed in different populations, These mutant loci are reported to interact negatively causing genetic incompatibilities in the background of hybrids when brought together in a common genome. In rice, two independent loci affect Hybrid development Gametes carrying recessive alleles at two loci aborted during development while the gametes of other genotypes were normal. Gene transposition, Transposable elements, Genome Dosage Imbalance, Genome Imprinting, Evolutionary Forces and Chromosome Rearrangements or divergent evolution among duplicate genes, is also a cause of genetic incompatibilities between isolated populations1
Incompatibilities in interspecific hybrids, expressed as sterility and lethality, are widely observed which causes reproductive isolation and thus contribute to speciation. Hybrid sterility hinders the transferring of useful genes between two species or subspecies and is a major obstacle for utilization of the potential heterosis in the hybrids. Identification and molecular characterization and analysis of hybrid sterility genes have refocused attention to the genetic basis of reproductive isolation. Although the present understanding is still rudimental and tentative, several conclusions can be drawn from the existing results. Firstly, evolutionary changes between populations can produce deleterious interactions which cause sterility in hybrids between populations. Secondly, genes involved in hybrid sterility may change their primary functions or genomic locations during divergent evolution. And thirdly, the factors that cause hybrid sterility are ordinary genes which have diverse functions without preference of special functional classes3.
References:
1.Shamoni, M. and Daniel, A. B., 2011, The Genetics of Hybrid Incompatibilitie. Annu. Rev. Genet,
45:331–355.
2. Tetsu, K., 2007, Reproductive barrier and genomic imprinting in the endosperm of flowering plants.
Genes Genet. Syst, 82: 177–186.
3. Yidan, O., Yao, G. and Qifa Z., 2010, Hybrid sterility in plant: stories from rice. Current Opinion in
Plant Biol, 13:1–7
%20(2).png)
0 Comments