Oct. 24-26, 2009, Yingjie Overseas Exchange Center, Peking University, Beijing, China中文版

Unique genetic behavior of nucleotide insertion/deletion in living organism

Dacheng Tian

College of Life Sciences, Nanjing University, Nanjing, China

Classical genetics is based on the behavior of symmetric alleles between homologous chromosomes during meiosis. However, the commonly existed insertions/deletions (indels) will break down the allelic balance between genomes, because these asymmetric sequences have no counterparts on another homologous chromosome. By investigating indels’ proportion in genomes and their genetic effects during meiosis, we found: 1) >20% of rice genomes are indel sequences, demonstrating that they are important genome components. The proportion of genes located in insertions is significantly different among functional groups of genes, suggesting that natural selection is responsible for maintaining such sequences; 2) a strong correlation between the level of genetic variation and the distance from an indel. Thus, we propose that heterogeneity due to an indel is mutagenic to surrounding sequences. The consistency of these patterns among different species suggests that indel-induced substitution is a general mechanism; 3) recombination rate is largely suppressed in the regions closely surrounding indels, indicating that this effect could serve as genetic isolation to maintain more diversity between insertion and deletion individuals; 4) insertions largely promote ectopic recombination for themselves, which could increase the genetic variation in both copy number and genome architecture; 5) a nucleotide dimorphism, a clear insertion and deletion haplotypes, is usually present around indels, implying a close association between dimorphisms and indels; 6) the conditional benefit genes (e.g., the resistance genes with fitness cost) is often present in some individuals but absent in the others, suggesting that the present/absent genome architecture is a result of adaptive evolution which is better to balance the temporally adaptive effect of these genes. All these genetic effects can only occur in heterozygotes or derive from them. The heterozygosity-related effects raise the intriguing possibility that the genetic variation in sexual species might be affected by population parameters, which will influence the evolutionary rates of individual populations or species.

Dacheng Tian

College of Life Sciences, Nanjing University, Nanjing, China

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