Bellwork: What is the human genome project. What was its purpose Bellwork: What is the human genome project? What was its purpose? Was it a success?

Studying the human genome Section 14.3

What techniques are used to study DNA? After discovering the importance of DNA, reading it seemed to be impossible The smallest chromosome contains nearly 50 million base pairs The job was made easier through the use of natural enzymes Enzymes can be used to cut, separate and replicate DNA base by base Allows scientists to read the base sequences in DNA from any cell

How do you cut DNA? Differences in the chemical makeup make DNA relatively easy to separate and extract from other cells and tissues Entire DNA molecules are too large – they need to be cut to size Many bacteria produce enzymes that do this – restriction enzymes Even the largest DNA molecules are cut into precise pieces - restriction fragments A few hundred bases in length Each restriction enzyme cuts DNA at different sequences of nucleotides

Separating DNA – gel electrophoresis Gel electrophoresis is used to to separate and analyze the differently sized fragments DNA fragments are placed at one end of a porous gel When electric current is applied, DNA Molecules (which are negatively charged) move towards the positive end of the gel The smaller the fragment the faster it moves End up with DNA bands based on fragment size Stains can make these bands visible

Reading the DNA DNA fragments are placed in test tube with DNA polymerase alongside the 4 nucleotide bases Unknown strand is used as a template A small number of bases have a chemical dye attached to them When these bond replication stops End up with a series of color coded fragments of different length Separate by gel electrophoresis again Order of colored bands tells exact sequence of bases on DNA Can be automated by computers – speeding everything up

Human Genome project A 13 year international effort with the goal of sequencing all 3 billion base pairs of human DNA, and identifying every human gene Other goals included Sequencing genomes of model organisms to interpret human DNA Develop technology to support the research Explore gene functions Study human variation Train scientists DNA sequencing was basis for human genome project First DNA was broken into manageable pieces By determining base sequences in widely separated regions they were able to use these regions as markers

Sequencing and identifying genes Once DNA is marked they used a method called shotgun sequencing DNA is cut into random fragments Base sequences are determined Computer programs analyze this data, and find areas of overlap Link fragments by linking overlapping areas Reading is not the same as understanding Scientists look for promoters to identify specific genes Sequences that separate introns and exons , and stop codons also all help in identifying genes

Comparing sequences Most of the DNA of unrelated individuals matches base for base with each other Only 1 base in 1200 will not match These are single base differences – Single nucleotide polymorphisms (SNPs/snips) Certain sets of SNPs occur together time and again – haplotypes (haploid genotypes) HapMap project started in 2002 to identify these in more detail

Sharing data Human genome project was completed in 2003 Copies of human genome are freely available on the internet More data is added on a daily basis Lead to a new fields of study: Bioinformatics – Where IT meets biology Genomics – study of whole genomes, including genes and their functions

What we learnt Only 2 percent of the human genome contains instructions for synthesizing proteins Many chromosomes contain large areas with few genes Half the genome is made up of DNA from viruses and other genetic elements Project was a great success Pinpointed genes Associated particular sequences in genes with numerous diseases and disorders 3 millions SNPS identified Opened up new avenues of research – biotechnology

Issues raised What happens next? Who owns and controls genetic information? Who should have access to this information? Insurance companies? In 2008 US congress made it illegal to discriminate on the basis of genetic information As science progress new laws may follow What happens next? Potential for tailoring treatments for diseases to specific individuals

Does it stop with DNA? DNA is coiled around protein clusters called nucleosome to form chromatin Where chromatin is compact genes are switched off Where chromatin opens up gene expression is enhanced Process of opening and closing controlled by enzymes that leave chemical marks, which are affected by stress, diet and disease These chemical marks are epigenetic – they are above the level of the genome They do not affect the base sequence, but affect gene expression These marks can be passed on to offspring