Microcollinearity in DNA Sequences of Small Genomic Regions, Gene homology, Centimorgan genetic distance, Homology

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Your Ad Here	Microcollinearity in DNA Sequences of Small Genomic Regions Studies on molecular maps across related plant species, as above, though revealed significant conservation of gene content, gene order and gene homology, this comparative analysis had its own limitations. For instance, only up to about one marker per 10 centimorgan genetic distance is available for comparative analysis, thus making it difficult to analyse small deletions, duplications and inversions involving only a few centimorgans. Moreover, many genes have multiple homologs within the same genome thus making it difficult to establish orthology between genes from different but related species.
In view of these limitations, in recent years, instead of markers, DNA sequences representing small regions of genomes have been used for comparative analysis, sometimes resolving what is described as microcollinearity. Although very few plant genomic sequences have been used for such a study, some patterns have been delineated on the basis of available sequences. Comparative analysis of gene sequences and repetitive DNA sequences has shown that they evolve at different rates. It has been shown that the gene sequences are more conserved, although disease genes have been shown to change rapidly. It has also been shown in several studies that the gene density differs and is related with genome size. For instance, at Sh2/A1 region, the intergenic regions were 7 times longer in maize than in the orthologous regions in rice and sorghum.
Similarly in 280 kb region at the adhl/u22 locus in maize, the genes were separated by more than 120 kb containing 10 retroelement families, but in sorghum the orthologous genes were only 50 kb apart. It has also been shown that microcollinearity may occur not only between related species but also between more distantly related species. For instance, in the adhregion, collinearity is greater between closely related maize and sorghum than between either of these two species and the distantly related rice. In contrast to this, wheat shows greater collinearity with distantly related barley than with the closely related rye.