The Preliminary Studies On The Comparative Genomics Of Dictyostelium Discoideum

The completed sequencing work of Human Genome Project had great Significance, signing that the new epoch of sequence study had coming.Through Comparative Genomics studies,series of unbeknown genomic secrets were discovered.This article compared the 13498 genes of Dictyostelium discoideum with proteins of 8 other model organisms,and cast light on the homology of proteins between them,provided new method and argument for evolution research of Mycology.D.discoideum genome is one of the most concise one.As a kind of cellular slime mould, it has become an eukaryotic model organisms for studying the key issues of molecular biology and cell biology.The whole genome of D.discoideum was released in Nature in 2005.It's haploid genome size is 3.4×107bp with 6 chromosomes,and the(A+T) content is up to 77.57%, encoded 12500 genes.Sequencing result also proved that D.discoideum has more recent homology with fungi and metazoan.The method of Comparative Genomics was adopted.All the datas were collected from public database.Standalone BLAST was downloaded as our search program,then our own database was established including 8 model organisms genomes,they were Haemophilus influenzae,Escherichia coliK-12,Sacharomyces cerevisiae,Caenorhabditis elegans,Drosophila melanogaster,Arabidopsis thaliana,Mus musculus and Homo sapiens.The results of BLAST were flat text,it's hard to select our needed information,so perl script was written to deal with our BLAST results.Genome characteristics of D.discoideum with 8 other model organisms were first compared, the results were as follows:1.From bacteria to D.discoideum,and then to human,the genome size increased gradually, signed that there was a linear relationship between organism complexity and genome C value.2.Contrary to genome C value,gene number and organism complexity had a nonlinear relationship.3.D.discoideum had the lowest(G+C) content among these model organisms,and was 17.87%lower than human's,which is contrary to the evolution order.We assumed this may has something to do with the proportion of encoded sequence and the optional 3^rd base of coden.4.The gene recombination rate might be low for genomes with short gene spacing,and the gene inheritance might be more stability.5.The protein diversity for D.discoideum needed to adaptive evolution might be produced from small gene repetition.6.Intron size determined the gene length.compared,the results were as follows:the protein homology between D.discoideum and H.influenzae was 11.8%,between D.discoideum and E.coliK-12 was 17.2%,between D.discoideum and S.cerevisiae was 36.4%,between D.discoideum and A.thaliana was 29.6%, between D.discoideum and C.elegans was 41.7%,between D.discoideum and D.melanogaster was 38.3%,between D.discoideum and M.musculus was 39.5%,between D.discoideum and human was 37.7%.