Section 14-3: Studying the Human Genome

Manipulating DNA The SMALLEST human chromosome contains 50 million bases DNA is a HUGE molecule that is difficult to manipulate In the 1970s, scientists discovered they could use natural enzymes to analyze DNA Today, scientists read DNA base sequences by using enzymes to cut, separate, and replicate DNA base by base

Cutting DNA Easy to extract/separate DNA from other macromolecules In order to analyze, DNA molecules must be cut into smaller pieces Restriction enzymes are produced by bacteria – they cut DNA molecule at specific sequences of nucleotides into precise pieces called restriction fragments Hundreds of Res, each cuts at different sequence

Cutting DNA Ex: EcoRI recognizes GAATTC Cuts between G and A bases, leaving “sticky ends” Can bond to complementary bases

Separating DNA Gel electrophoresis is used to separate DNA fragments that have been cut with restriction enzymes Can then analyze DNA in pieces Steps: Mixture of DNA fragments placed at the end of a pourous gel Electric voltage applied to gel, causing DNA molecules to move toward positive end (DNA has a neg charge) Smaller DNA fragments move faster/farther Creates a banding pattern Stains used to make bands visible Remove fragments and study

Reading DNA Read = sequence Single-stranded DNA put in test tube with DNA polymerase and four bases (ATGC) DNA polymerase uses unknown strand as template to make new strands Some of the added bases have dyes attached, Each time a labeled base is added, replication stops End up with a series of fragments that are color coded Separate fragments with electrophoresis, colored bands on the gel tell exact sequence of bases on DNA Automated

The Human Genome Project Began in 1990 – US and several other countries Goals: Sequence all 3 billion base pairs of human DNA Identify all human genes Sequence genomes of model organisms to interpret human genome Develop new technology to support research Explore gene functions Study human variation Train future scientists

The Human Genome Project How they did it: Break genome into pieces Sequence pieces, identify markers Used computer for analysis Current research explores data gained from HGP – looking for genes, identifying their function

Comparing Sequences Most of every person’s DNA is the same On average, one base in every 1200 with not match These are called SNPs (single nucleotide polymorphisms) Collections of SNPs are called halpotypes – haploid gentoypes Project called HapMap began in 2002 to indentify all the haplotypes

Sharing Data Copies of human/other genomes available on the internet New field borne – bioinformatics Combines molecular biology with information science Also new field called genomics – the study of whole genomes, including genes and their functions

What have we learned? Complete working copy of human genome in 2000 Full reference sequence in 2003 Contains 3 billion nucleotide bases Only 2% encodes for proteins Found genes/sequences associated with diseases/disorders Identified 3 million locations of SNPs New technologies, medical applications