chgenefunctionresearch基因组学说课.ppt

Chapter 7 Gene hunting and function research (2) Determining the Functions of Individual Genes How to prove the function of candidate gene? Find the gene responsible for the phenotype Expression patterns RNA expression assayed by Northern blot or PCR amplification of cDNA with primers specific to candidate transcript Look for misexpression (no expression, underexpression, overexpression) Sequence differences Missense mutations identified by sequencing coding region of candidate gene from normal and abnormal individuals Artificial interfering the expression of the gene* Determining the Functions of Individual Genes (p195~207) 7.3.1 Computer analysis of gene function Homology reflects evolutionary relationships Homology analysis can provide information on the function of an entire gene or of segments within it Homology analysis in the yeast genome project Homology analysis BLAST（同源查找）Basic Local Alignment Search Tool. Homology(同源性), similarity(相似性) and identity(一致性). Homology, orthology and paralogy Homologous genes are ones that share a common evolutionary ancestor, revealed by sequence similarities between the genes. Orthologous genes are those homologs that are present in different organisms and whose common ancestor predates the split between the species. Paralogous genes are present in the same organism, often members of a recognized multigene family, their common ancestor possibly or possibly not predating the species in which the genes are now found. Definitions from NCBI glossary Homolog: A gene related to a second gene by descent from a common ancestral DNA sequence. Orthologs are genes in different species that evolved from a common ancestral gene by speciation. Normally, orthologs retain the same function in the course of evolution. Speciation is the origin of a new species capable of making a living in a new way from the species from which it arose. As part of this process it has also aquired some barreir to genetic exchage with the parent species.