Presentation on theme: "Genome Projects A genome project is the complete DNA sequence of the genome of an organism, and the identification of all its genes Genome projects are."— Presentation transcript:
Genome Projects A genome project is the complete DNA sequence of the genome of an organism, and the identification of all its genes Genome projects are possible because of the large-scale, automated application of molecular genetic techniques (cloning and sequencing) There are now complete genome projects for all major groups of organism
Complete genome sequences NCBI genome website: http://www.ncbi.nlm.nih.gov/Genomes/index.html Total 908 species, including 172 eukaryotes, either completely sequenced or in progress
Which organisms? Pathogens - such as bacteria Model organisms - Drosophila (fruit fly), C elegans (nematode worm), mouse, which have been used in genetics for many years Agricultural organisms - rice, wheat, cattle Human
DNA sequencing by dideoxy method Copyright Bios Publishers Ltd
Technology Top-down for big genomes - based on first making a map Bottom-up or shotgun for little genomes such as bacteria Top-down approach uses bottom-up method on mapped bits of genome
Shotgun: contigs Contigs are identified from sequence overlaps In a bacterial genome, a specific 11bp sequence is likely to be unique (4 11 > 4,000,000) In human genome its 16bp (4 16 > 4,000,000,000) Copyright Bios Publishers Ltd
A model organism The Drosophila genome webpageDrosophila genome webpage 137 Mb of DNA on 4 chromosomes 13500 genes A view of the genome can be seen here...here...
The human genome The human genome webpagehuman genome webpage About 3000 Mb of DNA on 23 chromosomes About 35000 genes (only about twice as many as flies and worms) Most human genes have homologues in other organisms (vertebrates, insects, yeast etc)
Identifying genes with introns Copyright Bios Publishers Ltd
Variations in DNA sequence Because of shotgun sequencing, the genome was sequenced several times from different peoples DNA This allows DNA polymorphisms to be found The amount of DNA variation between organisms is a measure of how closely related they are It can be measured by comparing homologous genes (i.e. genes with a common evolutionary origin)…..
Homology - 2 DNA sequences with 80% identity By repeating this analysis over many loci you can get an accurate picture of the evolutionary history of the organisms Copyright Bios Publishers Ltd
The origins of humans There are 2 main theories on the origin of modern humans: –Multiregional: early human (Homo erectus) left Africa 1,000,000 Ya and evolved separately into modern humans in many places –Out-of-Africa: populations of Homo erectus around the world were displaced by the ancestors of modern humans, migrating from Africa 50,000 - 100,000 Ya These can be investigated by studying genetic variation in modern humans from around the world The Y-chromosome (passed from fathers to sons) and mitochondrial genomes (passed from mothers to all children) are often used for these studies
The multiregional hypothesis Copyright Bios Publishers Ltd
The Out-of-Africa hypothesis Copyright Bios Publishers Ltd
Molecular genetics supports Out- of-Africa Of all modern humans mitochondrial DNA, the oldest types are found in Africans By calculating the rate at which mutation has occurred (molecular clock) can see that our common ancestor lived 140,000 - 290,000 Ya