1 Review How do molecular biologists identify genes in sequences of DNA Use Analogies How is shotgun sequencing similar to doing a jigsaw puzzle 2 Scientist one day may be able to use genomics to alter a child’s inherited traits. Under what circumstances, if any, should this be used and when should it not be used? Write a persuasive paragraph expressing your opinion by using specific examples of traits.
Ch 14 Human Heredity 14.3 Studying the Human Genome
Restriction enzymes Cut DNA molecules into pieces, called restriction fragments, at precise locations EcoRI restriction enzyme Recognizes the sequence GAATTC Cuts each strand between the G and A “Sticky Ends” The single strand overlap. Cutting DNA
Gel electrophoresis Separate and analyze the differently sized DNA fragments. Separating DNA
Mixture of DNA fragments is placed at one end of a porous gel Electric voltage is applied and DNA molecules move toward the positive end Smaller DNA fragment move farther and faster. Gel Electrophoresis
Resulting pattern based on fragment size • Add stains to see DNA • Can remove individual fragments for further study.
Reading DNA • Single-stranded DNA is placed in a test tube containing DNA polymerase and the four nucleotide bases • DNA polymerase uses the unknown strand as a template • Add a small number of bases that have a chemical dye attached one for each base • Dye makes synthesis stop.
Result is a series of color-coded DNA fragments of different lengths Run gel electrophoresis Order of colored bands on the gel tells the exact sequence of bases.
The Human Genome Project • Main goal of sequencing all 3 billion base pairs of human DNA and identifying all human genes.
Researchers mark the DNA strands . Find the base sequence in different locations “Shotgun sequencing” Cut DNA into random fragments, then determining the base sequence in each. Sequencing and Identifying Genes
Computer programs take the sequencing data and overlaps fragments Align fragments relative to the known markers.
Look for a promoter Shortly after is the reading frame (become mRNA) Find start and stop codons, and introns and exons. Research Explores the Data from the Human Genome Project
Comparing Sequences • People have very similar DNA • 1 base in 1200 are different • SNPs (snips) • Place where there is a single base difference • Haplotypes • Closely linked SNPs that occur together • May help identify diseases and conditions.
Bioinformatics Combines molecular biology with information science Genomics Study of whole genomes, including genes and their functions. Sharing Data
What We Have Learned • Working copy of the human genome June 2000 • Full reference sequence April 2003 • 3 billion nucleotide bases • Only about 2 percent of our genome encodes instructions.
What We Have Learned • Pinpointed genes and associated particular sequences in those genes with numerous diseases and disorders • Identified about three million locations where single-base DNA differences occur in humans • Transferred important new technologies to the private sector, including agriculture and medicine.
New Questions • Who owns and controls genetic information? • Is genetic privacy different from medical privacy? • Who should have access to personal genetic information, and how will it be used?
President George W. Bush signed into law the Genetic Information Nondiscrimination Act, which prohibits U.S. insurance companies and employers from discriminating on the basis of information derived from genetic tests.
Modeling Restriction Enzymes • Write a random 50 base double strand DNA sequence using the 4 DNA bases. Include each sequence shown at least once • Make three copies of you double strand sequence on three different colored strips of paper
3. Use the drawings to see how the restriction enzyme EcoRI would cut your sequence. Cut apart one copy of your sequence 4. Repeat step 3 using the restriction enzyme BamI on the second copy and the restriction enzyme HaeIII on the third 5. Tape the single strand end of one of your fragments to a complementary single strand end of your partner
Observe Which restriction enzyme produced the most pieces and which the fewest • Evaluate How well did your model represent the actual process of using restriction enzymes to cut DNA. Contrast the length of your model to the actual length of a DNA molecule